Call a 2barrel gutless but, I once had a chevy 350 in a stepside, 4speed with a granny 1st gear. It also got 8-10mpg until I swapped the 4barrel holley to a 2barrel, started getting 12-14mpg. I believe my best was 16mpg at 55mph on a interstate trip. It also had headers and dual Cherry Bombs (opps,that dates me). I think it had a 3.73 gear, maybe 4.10 not sure. The OD tranny should help.