I recently purchased a 1963 Pontiac Grand Prix with no engine or transmission. I am wanting to put in an old school Chevy 300 engine and a 400 automatic transmission which is currently in a wrecked Corvette. Will I be able to do this without having to fabricate anything?
Short answer: no. There's always going to be something to fabricate, even if it's only modifying an engine mount. Is this going to be a period custom?
I don't plan on doing a show quality renovation. Simply going to replace worn or missing parts.. I eventually want to use it as my daily driver.
You can go all the way up to a 455 Pontiac motor with minimal bracket/mount changes. A 400 trans will go in as well, but you may have to modify the tunnel above it a smidge as well as fabricate a mount and a new driveshaft. I put a '72 400 motor in my '64 with the matching TH400 trans. Had to enlarge the tunnel a little, add a 1/4" plate extension to the trans mount bracket and get a new driveshaft. Everything else pretty much just dropped right in the hole.
If you want it to be a daily driver with decent gas mileage, forget the Turbo 400. Its definite overkill for a 300 cu in engine. Also it takes more HP to actually operate a 400 trans, so your engine will "automatically" consume more gas. Best bet is to get some type of overdrive automatic. As for engine choice, a 300 (305/302 ?) isn't going to provide much torque, and the lower 1st gear of most overdrives will help you. All of that being said, a 350 Chevy won't cost anymore than a 300 but I think you would be better off with some form of Pontiac motorvation. Takes a little more looking but they aren't that hard to find. It sounds like you may know where you can get something cheap already and thats why you are considering that swap. Personally I would not go that route even if you have to spend more money. Scan Facebook Marketplace for a while and see what you can find there.
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