The Stovebolt Site Forums The Parking Lot '60-'66 Trucks big block

No doubt this has been discussed a hundred times but truthfully I don't get on here much unless I have a question or need to research some ideas. I still have my old 61 half ton long bed GMC that has a tired but running 305 V-6 and 4 speed in it. I drive it from time to time but usually hold it to around 65 mph on the highway to keep from stressing the old engine because I know how hard it would be and expensive to get parts to rebuild. anyway I recently was offered an old chevy 1 ton that has a rebuilt 454 with not a whole lot of miles and the 4 speed it came with. I'm thinking about getting it and possibly swapping the engine and trans.no doubt the rear end would be a weak point if I really hot rodded it but running empty on a long bed I expect the tires would break loose way before the parts would break.I just wonder if physically it would fit without a lot of surgery and if it would weigh that much more than the monster 6 that's in it

Hy Skelflyer, I will begin my comments by admitting that the early 60s and V6 GMC engines are not my area of expertise. I believe from 1960 to 1962 the engines were mounted using a three point system, one mount center front of engine and one mount on each side of the engine at the bellhousing. The later 60s engines employed a four point mount system, as the big block Chevrolet engine was not released until 1965 I do not believe there are any factory parts to mount the big block Chevrolet engine in the early 60s chassis. As to engine weights I believe the GMC V6 and the big block Chevrolet V8 would be comparable in weight. I do not think the Chevrolet big block can be swapped into the early 60s chassis without some engine mount fabrication, hope that helps.

Justhorsenround/Martin is installing a SBC in a 62 GMC. See his post in this forum. I have a 1960 GMC 4X4. The BB GMC is about 800 pounds wet. A VERY heavy motor, The BBC is not near that heavy. The V6 is mounted, as you know, with rectangular pads on each side and bell housing is supported on feet with tranny cantilevered. Again, as you already know. The mounts and their brackets must ne removed. You can use "perches" or aftermarket Chevy mounts for the BBC. Martin is in the midst of doing that and has good info in his post. It will take a decent amount of work. The torsion bar in 60-62 does not help any.
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Don't worry about the V6. It is well built and will last much longer than any other motor of it's day. It is a boat anchor but I decided to keep it in my 60 because of it's originality and after you read up on it, it grows on you. It's bullet proof. I am a 454 guy all the way but in this case I got a soft spot for this overweight monster. It is a 4000 RPM max motor. If you are cruising at 65 and are happy and at a good RPM, you are good to go.
Otherwise let the V8 fun begin. Whatever you do, GET THE 454 and keep it. The older ones are getting a little hard to find. If the 454 is "aluminized" and has an aluminum bell housing it will be Waaaaaaaaaaaaaaaay lighter than the V6.
GMC used Dana 44 diffs. That will be OK for the BBC. Keep in mind that high cruise speed is all about the trans and rear ratio (including tire size). Hot off the line is all about cubes and trans/rear ratio. Hooking an O/D to a 305 may be a real challenge. I don't know what kind of "performance" you seek.

Don't get all giggly over the word "rebuilt" on that 454. To me that is a red flag unless I know who did it, their experience and if they did it in the dirt or in a clean shop.

If the V6 has good compression, not much smoke, no overheat......it's good to 250,000 +.

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thanks for the replies, and the old 305 probably uses a quart in 700 miles.I used it for a week driving 120 miles each day round trip hauling a welding machine bottles etc on a skid I built to slide in- I stopped at the same station each day and it held 10 gallons to top ooff so it gets an honest 12. has an aftermarket holley 2 bbl. that was kinda grungy but I cleaned it up. and I doubt the 454 would beat it any on mileage. it has the old GMC rear end that checks to be 4.10 ratio. I would not do more than an engine swap and at this point it probably doesn't make sense unless it's just to say I did. doubt I'd gain mileage and might even be worse with no overdrive. just a straight truck 4 speed.I do know of the fellow that built the engine so I would not be concerned it it checks out OK. I can run it in the truck it's in.but I'm not going street rod with it and better keep what bucks I have

Slelflyer, the biggest challenge I faced was the x-frame crossmember. I am putting a 700r4 behind the SBC and the old 3 speed mount was not going to work. I had to cut it completely out and fabricate a new one several inches farther towards the rear. Not a problem just time consuming. The other issue is how the engine mounts at the front. The 60-62 series mount at the front of the engine on a plate riveted to the front crossmember. The later SBC/BBC Engines Mount on the sides of the block. The frames are not drilled for the later mounts and a later mount will not fit the frame. Aftermarket mounts are available and require you to mount everything to the engine then drop it into place. Then mark for drilling the frame and pull the engine back out. Drill your holes and put the aftermarket mounts in place. Now your ready to put the engine back in. Be ready to fabricate lots of stuff. Nothing that can’t be overcome. Just a large PITA.

My father ran an LS-6 454 (450 hp) in a half ton 66 GMC with a stock (Posi) rear end with no issues. It had a NP top loader 4 speed tranny. He ran it hard leaving lots of black marks on the street. I eventually got the truck and ran it with various 6 bangers and small blocks before my wife made me sell it. It survives in Florida now.

The 454 is most likely lighter than the old V6 and FOR SURE will get better gas mileage.

Unless the GMC bellhousing crossmember is different from the Chevy ones, you can look for a chevy cast iron bellhousing, and use your same trans. They also made that same style bellhousing bored out for the larger input bearing retainer of the sm465 (you should have a 420 right now unless someone has swapped it out, the 465 is what they started using after the 420 and probably what's mated up to that 454 with the aluminum bellhousing).

If it was me, I would:
find a cast iron chevy bellhousing that will mount to your crossmember
yank the v6
swap the bellhousing
drop in the 454
fabricate side mounts or a front mount for the 454

That way you don't have to move the transmission, cut out the bellhousing crossmember, shorten or lengthen your driveshaft, etc.

I second the cast iron bell housing but would use the truck one as it takes easier to use motor mounts. With the rear mounts on the bell housing you can use front mounts on the engine which is sometimes easier. IIRC the 454 doesn't have drilled and tapped front mount holes but does have the flat spots so do your own. I am using my last iron bell housing on a Mercruiser (Chevy II) engine that's going into a 1928 Chevy dump truck and will for sure have to pick another one, or two, up at a swap meet. They are handy for use on the engine test stand and the horizontal mount starter has saved several engines with broken a starter mount ear.

Here's another vote for using the original bellhousing, but for a different reason. The 60-62 Chevy's ,and probably GMCs, used a hydraulic clutch system. Keeping the old bellhousing will keep you from having to reconfigure that as well.

I wouldn't get too exited about gas mileage. The factory 454 trucks I had would get a solid 10 mpg, didn't matter if you were going uphill, downhill, loaded, empty. One was throttle body injected with 4.10 rear end no overdrive, another was Q-jet, 3.73, no overdrive. The only other big block gas I had was in a '67 1/2 ton, 396 with a powerglide, in 1971-72 gas mileage was not my main concern, I was just thrilled to have wheels to get to school and work. Now my crew cab dually 4wd 6.5 diesel with 4.10's and overdrive gets 18mpg, 7000lbs empty. I'm happy with that.