Tiller Question
 

I have an 1812 and a 2072 which tiller should I start looking for and for which tractor. I have a homemade sleeve hitch on the 1812 I'm going to add a Cat 0 3pt to the 2072 someday...Thanks

Without some pretty good amount of work, there is only one tiller that will fit on the GT, none for the SGT.

The tiller for the SGT requires 3pt and rear PTO.
The tiller that fits the GT has it's own engine and needs either a sleeve hitch, or rear 3pt. You can adapt an older tiller (#1, 1A, 2, 2B) to work but it takes quite a bit of mods. I've done it. Here's the thread.

What's the difference in the 1a 2b etc. ?

#1 is the first tiller. It was only like maybe 20" wide as a "base model" but you could add extensions. One, or two depending on the HP of the tractor running it. I don't know what the difference is between the #1 and #1A. The #2 was made as a "base model" the width of the #1A with both extensions. The #2B was the same as the #2 but could be used with either sleeve hitch set-up or Cat 0 3pt. Although when using it with 3pt, it didn't utilize the lift arms, just the rockshaft, and you had to use an adapter to connect the lower gearbox to the 3pt rear cover plate.

The 2B also had the larger pulley's for the 82 series, 5/8 inch, for the gearbox. They could easily be swapped out for a different pulley though.