the fuel mileage is always going to be horrible.

that being said, i would change out the manifold to a good dual plane like the Weiend Stealth or even Edlebrock Performer RPM or air gap. the Torker II is a single plane intake more suited to high rpm usage. the dual plane intakes sacrifice top end for more usuable low and mid range performance, the rpm range most people drive in.

as far as the carb, the Holley is a good carb, probably just needs to be tuned and dialed in. either do some research on the net about tuning the holleys or take it in to a good performance shop to dial it in for you. they are not that hard to dial in properly. the Proforms are also a good choice along with the Edlebrock/Carter carbs. the Edelbrocks sacrifice some hp but get better mileage and driveability(maybe .5 mpg give or take, we still are talking a 460 here) and seem to keep thier tune for longer than a holley.

that would be my suggestion to make the truck a little more friendly on the street.

Rgds
Mike