HELP! I bought a mess?

WOW!!!! IDK...I would think about using what you have to keep it original. OTOH, you should be able to use a 318 that you have and those heads and build a killer on the cheap. You could buy a 4 inch stroke crank and end up at 391 CID, assuming a .030 overbore.

Those heads, a nice tight lash solid lifter cam (you already have the rockers) and a 3.55-3.73 gear and you have a super nice iron ball tire tire smoker right there.