The Select-A-Speed Drive Kit was model #TA10 and was available for a suggested retail price of $99.50. It gave standard speed or 2 to1 speed reduction. You're real lucky that, that thing didn't wind up in the metal dumpster at the local land fill.That's what usually happens to things like that when people don't know what they go to and just want to get the garage cleaned out.
I saw that a while back when I went to the dump to get rid of some stuff and saw two old garden tractors sitting on top of a full scrap metal dumpster! One was a Wheel Horse and the other was a John Deere (a 110 if I remember correctly) I didn't have any way to drag them out of there but at least they let me get the rear wheels off them. Lucky for me the tractors were laying on their backs, so the wheels were easy to get to. I used them to make one set of wide rims for my T-758 puller.
Make sure you replace the front bearing in the casting now or you'll be tearing it apart again later. It's a sealed bearing which is still available and not hard to find. I can't remember what the part number is but you'll find it stamped on the edges of the old bearing if you look closely so don't beat it up trying to get it out of there. You'll be tapping it out from the inside anyway. When I got mine all back together and mounted on the tractor, I filled it with 90w oil until it started to run back out the drain plug in the front of the casting below the shift lever..
The Select-A-Speed will make a nice addition to the Panzer and is a good attention-getter. Good luck with it.