Slant Six to Big block Engine swap in a 74 dart sport.

I recently bought a 74 dart sport for a grand and was oringally going to just do a small block swap but having a heck of a time finding a 340 or a 360.But have quite a few big blocks laying around.I see schumacher makes a conversion kit for it.And from my understanding you wont have power breaks which isn't a big deal since my car dont have it anyways,but what my concern is I want to keep power steering and the cooling system up to par with a big block and the front end componets to carry the extra weight.Would I be better off with a b-block or just go with rb block.And I would like to some trick tips and any advice to go about doing it.Thanks for the help guys.
Erik