Kenmore Heavy Duty 70 Series washer

I purchased this washer new in 1992. I replaced the timer a couple of years ago. That is the repair history. A few months ago I found a retaining clip under the washer but had no idea where it came from. The basket quit spinning recently, so I figured it was the motor coupler. I did a full disassembly, replaced the coupler, although I am not sure the original one was shot. During this process I noticed where the retaining clip came from, it was originally on the bottom of the drive tube. There is not anywhere on the bottom of the drive tube for this clip now, it appears that this has worn down about 1/8" or so. I noticed the plastic brake disengager was melted some and rather mangled. I located a new drive tube assembly, complete to the clip. I removed the old drive tube and installed the new drive tube. After most of the reassembly is complete, I can not get the big nut installed on top of the basket, and if I try to install the agitator over this poorly installed big nut, there is not enough spline showing for the agitator to fully drop down and be installed, it is clearly setting to high off of the basket. It seems that the transmission shaft needs to be extended about one inch. I did another disassembly to check for anything out of the ordinary, but did not find anything. I did another reassembly, to the point of securing the basket with the big nut, but there is only about one inch of spline showing. I have to be missing some simple step. I am by no means qualified to be working on this. I just happen to have more time on my hands currently, with the economy. I prefer to make my own repairs, when possible, for the education of how things work for future repairs. Any ideas?