Thanks folks, I truly feel fortunate.
Update: Gwen is doing great this morning. we did our walk around the block. A lot slower, but we did it.
Yes, this was a treadle, and hopefully will be again.
I have a friend who has been in the collectible sewing machine "biz" for decades and I asked if there was a chance. He said "Those are super super rare, I know One person, I'll ask" about two hours later I got a reply saying "Ok, I was just laughed at by my source.... He said your bes bet is to take a standard treadle and cut it to fit"
YIKES!!!! No way in hades I am cutting up my other G&B Treadle to make this one work. Besides, I have a plan....
I figure if i get the shelves out, and map the original base mounting holes, i can put a board in the bottom using the original holes and then mount the replacement into the new board. (Thus allowing it to be removed and returned unharmed to original should the fates favor me again with the discovery of an original set)
Underside pics to follow soon.