Instead of going to a V-8, why not scavenge up a 292 somewhere? It will work better pulling heavy loads than the small block V-8, because the low-end torque is better. With the exception of a little motor mount tinkering, it will be an almost drop-in fit. Get a bigger radiator to handle the extra heat load, though!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!