Can anyone help me.  I want to Find a diesel engine to drop into this Chevy.  It orig. had a strait 6 at 325 hp.  What would i need for diesel?  

If you want to keep it GM, I'd go with an LBZ Duramax. Bone-stock, they're 360 hp and 650 lb./ft. I'd try to get either a complete donor vehicle, or at the very least the engine & trans together.

If you don't care so much about brand loyalty in terms of the engine, you could swap a Cummins into it. They're real workhorses, and there are plenty of parts out there for 'em.  

A straight 6 at 325hp? in 46? You sure that's not a 235ci?
Anyway.....I agree with E. The Duramax or possibly a Cummins(4 or 6BT, but either may be tricky to fit. I've had a 54 Chevy 3/4T before, and I know the engine compartment is rather small & narrow. Perhaps a Detroit 3-53T.