Am I correct in assuming that all '66 and up 23 spline 4spd main shafts are interchangeable? Can a old style syncro rings just be interchanged with a newer style or is there more to it? I'm trying to swap out the guts of a 4spd out of a 68 Roadrunner that has a larger input shaft bearing into 73ish? 4spd stamped PP8334262. The main bearing in the 68 (right) tailshaft is smaller than the 73 (left) go figure. Can anyone tell what correct bearing is for the one on the left?