'75 360 Rebuild, Cam?

I have a 70 Duster this engine is sitting in. 727 with 9.5:1 pistons. The Rear Gears are 3:55's. The tires are at 27" Dia. right now, but may go down an inch or two. These are 60 Series, will be putting on 50 Series in place of them, 15" Rims. The car, with me and tools weighs about 3,200lbs.

I just got an AirGap Eddie, will be using my Holley 600 CFM 4150 (Mech) and standard headers, Electronic Ignition/Better than Stock. I am not a cam expert, but I would like to have a hydraulic roller cam as big as I can get for the street. Don't plan on using the Duster as a daily driver, just for fun. But I don't want to only get 8mpg either. It gets 12 or so at 65 on the highway now with the above and a Performer intake and very mild cam. I do understand I will lose mpg, but don't want it to take a serious dive. What is a reasonable expectation for mpg with a decent cam?

Anyone have a suggestion for lift and duration? I would like to have a cam mfg & prt# if you have one. I "think", not sure, that buying a kit would be most economical, but I notice not all mfg's offer one for every cam. As long as the required spring prt numbers and other assembly numbers are available, I can find them or ask the mfg if I have a cam mfg and prt#

Thanks...