[thatguitarguy]

Originally Posted by mpvue

I don't see why you'd suggest a 2bbl; a properly sized 4bbl will be ruuning most of the time on its primaries, which are smaller than the openings on a 2bbl. then, under load, the secondaries open up. a vacuum secondary carb only opens the secondaries when the vacuum signal drops, and this point is adjustable w/ springs.
years ago, I was able to tune my Dad's 460ci F250 for a few extra mpgs by putting a heavier spring in the carb; IIRC, he went from 9mpg to around 12-13.
even better than a carb in this application, there are myriads of fuel injection kits for chevy V8s, from simple TBI setups to full blown laptop programmable rail injectors.
as for the transmission, there are stout overdrive units available as well as modern computer controlled 4 and 5 speed automatics.

Do you have more info on the spring swap? Would this be similar on a Chevy? For me, this sounds like a better starting point than a full induction swap.