Ive had the right side off once, by myself (nobody here to help) except some chains, straps and a machine that can lift the entire dozer. Your right about the time, however, why would a track and chain cause pulling? I could see frozen pins binding, however ive driven it far enough to sort of break things loose.
Im thinking if its not that terrible weld job someone did on the frame where it connects; there is a broken planet gear in the rear diff thats causing the power differential to not be 50/50
I would think if you had any damaged or broken gears you would have heard some grinding or have some metal in the fluids showing...if its not a horrible fix to grind the weld off and properly line up the parts , try that first, you spent plenty of time and $$ fixing it up, for a little more time and effort to get it going straight is worth it before giving up..