I think a 400 will be easier to find parts for later (beacuse its a more popular engine as it does have more opportunities for 'enhancement = more hp)....a stock 400 isnt that much more HP than a stock 350...but either (Pontiac engines) will work fine...installing a Chevy 350 or such you will have to adapt a few things , meaning ,you need to do more work to install it..it 'may' be easier to find a Chevy engine though and possibly cheaper , but in the end it will also be worth less when its time to sell the car....if you want to step out of the box (like with a Chevy engine), step a little more out and get modern engine , like an LS1 or such...just my 0.02