What will fit / work?

I've been kicking this around for while, It has probably been asked before, but here it goes again...I've got a 1965 Barracuda, that I want to "street rod." I've got a low mileage 273 that I've been accumulating stuff for, (heads, hi-po pistons, intake manifold, rockers and grooved shafts, etc.) however, the closer I get to starting the build, I think about a 318 or 340. My question is what year and model 318 or 340 (maybe 360) will fit my car without major modification? BTW, I also have a 8.75, with a Richmond Locker (4:56) and a A833 going in it.
Thanks
Norm

What are your plans for the 273 stuff? I might be interested.

David