you don't have to do anything to the rear end to change the trans, and if you want better highway speeds at lower RPM, the choice is what OD - if you could find a factory 3spd OD [68 up] it'd be a bolt in swap, no changes required .... a 5 speed would be next easiest, no clutch change required, but you'd prolly need to lengthen or shorten the drive shaft, and maybe change the yoke as well as rig a floor shift .... a 700R4 would be fine, likely still require the driveshaft adjustment, and you'd need to rig a shifter that has the gear indicator, a column auto shift from 67-72 could be adapted
Bill
