I'd put a 360 in it. Like 66sportfury said, you can keep the original drivetrain if you ever want to return it to original. You can use the slant six K member and use motor mounts from Schumacher (they're on the internet). If you don't already have discs on the front, pull them off a later model A-body ('73 and up?) at the wrecking yard. It's a worthwhile upgrade anyway. You might be lucky - the front end I got to replace the drums on my Duster came off a Gold Duster. Grab the proportioning valve too - you'll need it. And if you have a 7 1/4 rear end you'll need to step up to an 8 1/4 at least to handle a V8. Again, it'll give you better brakes on the back and unlike 8 3/4s they can still be found under A-bodies in wrecking yards and it'll bolt straight in. Or move the spring perches on a B-body 8 3/4 and use that. Some wrenching, mostly wrecking yard parts with a few aftermarket parts and you'll have a fun car that'll stop in the wet
