I had a gm that keep getting better milage in a heavy truck 305 cu in it with a over drive trans up near 30 miles per gallon about 6 months later I found out why it got so much better / it started popping thru the carb at light throttle yes the cam was wiped every lobe was rounded off evenly like it was made that way so go low lift and you will be there. find some 1.4 rockers