Rocker Arms Ratio

my calcs show the new lift would be .530/.542, basically no change from D.Hearnes but slightly more precise..... also the 1.7 rockers will have a small effect on duration too so you may notice a slightly more burbley idle too.

milling the heads will have an effect on power and mileage because of a bump in compression. however i'm not sure how much you could ump the compression and not have detonation issues. generally you'll be good with a 10:1-10.5:1 or so on pump gas, though with your iron heads i'd shoot for closer to 10:1 or so. you might be able to get away with 11:1 or so on pump premium with aluminum heads. if we could just get E-85 around here you could get away with 11:1 or even higher with iron heads

If you really want a mileage increase, a switch back to the factory roller cam that engine came with is what you want. Combined with the 1.7 rockers, it's an outstanding cam for smooth power and mileage and the closest you'll come to having EFI performance with a carb.