Welcome to FTE and the Virginia Forum,

I don't know the answer to the emission question, but maybe doing a tune-up (plugs, wires, distrubtor/cap, filters (fuel and air), etc... could help with gas mileage.

P.S Just a little FYI, there is a lot of info on the FTE Site, and a lot of intelligent people on the different forum pages, maybe posting in the 460 engine forum, somebody could further help on both gas mileage and emission questions.