You could probably pull 13 - 16 mpg on the highway if the car is geared tall and you're on reasonably flat ground.
PontiacDave - From the pics of your Grandville, you could probably buff that paint out. Buddy of mine used to detail cars, he would use some special waxes dealerships use (3M was one of them) with a high speed buffer (not those $20 Wally World ones) You have to be careful with the high speed ones not to burn the paint, but the difference is night & day.
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Two 1975 455 Grandvilles &
'79 455 Trans Am
‘69 Camaro SS 396/375 (owned since ‘88)
‘67 Corvette 427/435
‘23 Lexus LS500 awd
‘20 Audi R8 & ‘25 Toyota RAV4 (wife’s cars)
‘95 Ford F250 4wd 7.3 p-stroke
& countless Jeeps & off road vehicles & motorcycles 
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