Hi Crazy,
You did a very nice job with the Ol' Troy-Bilt. I almost bought one at an estate auction before I bought my first BCS, but quit bidding at $300 and the winning bidder got it for $325. It was an older Horse, but I have no recollection if it was a Horse, Horse II, or Horse III. At that time, I didn't even know they had PTO models.
I know very little about Troy-Bilt tillers, but had thought the engine had to be 3/4 inch shaft to fit a special pulley made for the reverser. How did you get around this? Are you planning on building a bigger tiller to accommodate the nearly double HP you now have?