If you have your heart set on using the C-6 you have
the bolt pattern on the trans will dictate what engine you will use.
The 302/351 uses one pattern, the 429/460 uses another pattern, and the FE 390/428 uses still another pattern.
They are not interchangable.
--Mike
PS THe worst engine you could pick would be a 1 cylinder crude
oil buring World War II vintage liberty ship engine.
1)price: really expensive
2) performance: slow to rev but good torque
3) aftermarket parts: none. Hell there are no factory parts either!
4) weight: you might have to modify the fenders and change the front springs (about 30 tons)
one problem would be the trailer hitch needed to tow the crude
oil fuel bowser behind you