welcome, the 400 motor is a good choice.chev being the smallest,size is compact and will go fairly easy, v8 crossmember is a must for motormounts.pontiac or olds will fit but needs more work,relocate stearing box ect.years ago my dad fit a 303 olds in 53 gmc 1/2 ton.he made exhaust manifold for left side to clear stearing box.best of luck with your bolt