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I have a '62 C10 with a 235 and would like to upgrade to a bigger 6. My problem is that I don't know what is the best choice: 261 Chevy, 270 or 302 GMC, or a 292 Chevy. I was surprised to find this truck has no provision for side engine mounts (no holes in the frame). Althought I think the newer 292 might be a better choice, I can see there might be engine mount problems. I'm open to suggestions.

The 261 would be the easyest to put in but are hard to find & would probably need rebuilding. I would put a v-8 in it. It was an option so all stock parts would work. It all depends on what you are capable of doing. You don,t want to get in a jam although you have plenty of help available on this websight.

I have put 292's in several old trucks. I got the motor mount perches from a donor truck, positioned the engine with my hoist and then cut the perches to fit. I drilled holes in the perches and the frame and bolted them in. With an RV cam and a later carb they really do the job! Redcoat

A V-8 would be logical, but I just have this thing about wanting a 6. From what I have seen, the older sixes (261, 270, 302) are hard to find. I do have space and most of the tools I need to make small modifications and have done some fabrication. My other project is a '57 Chev 210 Sport Coupe and my driver is a 31 Olds coupe.

I also have a 62 C10 with a 235, 4 on the floor, posi, with fentons. It's good to see you want to stick with a 6. I've always heard that a 302 is the motor to build if you want a 6 that can embarass a v8. Good luck!

I have a 270 and it performs great in normal driving. Pulling a trailer it doesn't have the grunt I want, but that is probably my 3.08 gears as much as anything.

I don't think the big GMC motors are as hard to find as you might think. I've had a couple come and go, and have found others without looking.

Just let people know you're interested, and if you're a little patient you'll have one.

You can find 261 short blocks and cores in junk yards or buy one from Langdons. The main difference between a 261 and a 235 is cylinder bore, one is 3 9/16 and the other is 3 1/2, or something like that. The later 261 also has a fully flowing full pressure oil filtration set up that none of the 235's came with.

Since the 235 head, crank, rods, cam, bearings, etc...all fit on a 261, if you've got the choice and plan on building, get a 261 block and the rest of it is easy to come by.

One thing to keep in mind when looking for a replacement 235/261 to build is that they also came in some cars (261's in canadian production sedans and not US). Many of those have side motor mounts set ups, so you'll have to use the bellhousing and front motor mount on whatever you are getting rid of. There is a great article on Patrick's website about the swap.

My advice is get a 292 and forget about all the rest,except 302 GMC that are scarce.

Gm improved them by putting 7 main bearings on the newer sixes starting in 1963 they are smoother running engines and cranks are steal in them till 1966, and best of all they will fit all GM Vans and trucks 66 to 91, so you will not need to do a micky mouse Job trying to make them fit.
If you want go with an old one get a 302 GMC make sure its not a 270 cause they look the same.
Those 302 GMC engines will still have value in the future them others 235 261 270 will end up going to China and comming back as action figure toys or Toyota Echos.

The gmc 302s are a dime a dozen. At least the military versions are. Look for a Korean era 6x6 military truck. Those trucks sell for very little money on ebay all of the time. Dozens sell at GSA auction for $50 bucks each. They are not rare.

You can buy NOS 302 cylinder heads today for $150.

Vendors sell low mileage (<20k) long blocks for $800.