The Stovebolt Site Forums The Parking Lot '60-'66 Trucks SM420 to a Pontiac

I'm thinking about replacing the 283 in my '62 with a Pontiac 400, will the Pontiac bolt up directly to the SM420? I'm guessing it would since GMC used the early Pontiac V8's in their late 50's trucks.

The pontiac 400 is a different breed than the SBC. You will need a pontiac bell housing for sure.

Thanks, 'mater. So with the Pontiac bell housing I can bolt up to the SM420?

I think so, but don't take my word for it. All I know is the bolt pattern to the engine side is Pontiac only.

Seems as though a better selection of transmissions would be available for an engine like the Pontiac 400. How about a Turbo 400. Or maybe a Muncie if you like standards. A built 700r4 would be a nice combo. Just thinking out loud is all.

This is for my work truck so an automatic isn't what I'm looking for. The reason I'm looking at a Pontiac is because that's what I have a good 400 laying around. Figured since pontiac motors make good low rpm torque and get decent mpg with a q-jet that it would be a good replacement for the 283. Keeping with the GMC late 50's theme...

My dad had a friend who put a 389 in a 56 Chevy 2 ton log truck, back when the truck was pretty new. It ran like crazy and pulled stronger than anything around for a little while. Then they learned why truck motors have lower compression, when it broke several pistons on a long hard pull. I still think for what we do with our old trucks it's a cool swap. Remember, the big motor for trucks back then was a Buick 322.

The 400 will not fit the GMC bellhousing,the 389 will till about 1960.Pontiac changed the bolt pattern.

That's good to know about the bolt pattern. I also have a good '66 389 available. I probably should've said that my truck is a Chevy.

Pontiacs make great motors for trucks, but the parts to put them together are extremely limited. The main reason they are overlooked is because they will not simply bolt in. The problem lies with the bellhousing. Our trucks used the bellhousing to secure the engine. The bellhousing is the rear mounting point of our engines. I'm not sure if you can find a pontiac bellhousing that will bolt to your crossmember other than the 55-59 gmc v8 bellhousings. That would limit you to using a 55-60 motor. Of course you could always fabricate new mounts.

PM me if you need an alluminum bellhousing that will bolt up to the poncho and the sm420. As stated above more fabrication will be needed to make this bellhousing work.

I have a 59 pontiac 389 that has been bored and stroked to 447 inches in my 59 gmc, but the engine itself was a bolt in swap for the 336 gmc v8 that was in there.

I'd sell or swap the 283 and 400 for a 350 sbc. The poncho swap just sounds like alot of headache for the end result. What year 400 is it?

It's a '71 400 from a big car.

swingdaddy, now you've got me thinking. My neighbor has a spare 347 sitting in his garage that he'd let go pretty cheap. Supposed to be a runner and complete except for a couple brackets that he robbed for his '57 Chieftan project.

pm sent.

347 is a good motor. The main bearings are smaller than the typical 3 inch mains of a Pontiac 389. The 3 inch mains are preferred by many engine builders. I believe a 1957 347 would be a step backwards for your 1962 with a 283.

Your 283 bellhousing will bolt to any SBC or BBC motor. I dislike the chevy V8s for being so common, but in your case, A chevy v8 will be the easiest and cheapest to swap.

As stated the pontiac swap is doable, but it will require fabrication.

Ok, I was thinking about this Later pontiac swap and I thought...
Perhaps you could make or use an adapter plate to bolt your bellhousing up to the pontiac motor.

Companies like this one http://www.wilcap.com/webdoc8.html make adapters to use mate different transmissions to different engines.

http://www.jegs.com/i/JEGS/555/60170/10002/-1?parentProductId=751074 This might actually be the plate you need to put the chevy bell on the pontiac. You might also need a spacer plate to push the flywheel back the same distance.