72 electra, 455, turbo 400 trans, probably a 2.73:1 rearend, will go 18ish on the hiway and 10-13 in the city.
I had a 72 olds ninety-eight(basically same car) that got the above mileage, untill i put a cam in it and had the heads milled with a re-jetted carb, then it got about 5 mpg in the city(i couldnt keep my foot out of the gas!!!!!!!!)