my 64 f100 has a 3 speed in it and a 9 inch rear . My ? is what gearing is my axle and what would be the best gearing to put in it to get better mpg. also i have a 9 out of a 79' pickup that had a 351M in it w/ a 4 on tha floor would that gearing do any better and wud it bolt straight up? can u even tell the gearing by this info? if not what u need?