Not only am I going to have to, : ) but I made a lot of progress yesterday. Got the split master pin out, pulled the track outside with the lawnmower, took about an hour to get the track frame off as the inside was dry dirt, and the sprocket was loose. Now it's time to weld some heads on to the rusted out bolts and see if I can get the final drive assembly loose

Sounds like mine Gary. My left side brake pedal shaft was broken, and the brake band itself is broken. Just about every bolt on this unit is seized so I've been getting plenty of practice at extracting them : ) My wish list would be a drill, mag or something with a ten-way adjustable mounting block that can center and align into any angle and position and can take 1/8 twist drills up through 3/4" annular cutters (that need no lube or coolant) - ah dreams.....
I'm guessing the teeth being missing is a combination of wear on the brake hub splines and the plate teeth, and/or the plate teeth and the inner hub splines. Either way, all of those parts will be replaced with new, that's no problem. The bigger problem is my track frames are very flimsy from being rusted out - previous owner obviously never cleaned the track gear at the end of the day - so I need to find a wreck that is 5U13273 and up for the correct length.