I do a lot of sympathy bidding at auctions! I've gotten some very interesting items that way. This one, I'd have bid in a heartbeat! I have a considerable collection of "conversion tools" (things that attach to a drill, and make it into something other than a hole-boring device). I do NOT have this one, though, nor anything from Greene. I've got some very similar (probably have close to 20 different sabre saws, going back to a "WYCO" [Wyzenbeek & Staff Co.] that was shown in at least two magazines in 1930-31. The patent was applied for in January 1930, issued in 1932: Popular Mechanics Nov. 1930 p148. Pop. Science Jan 1931 p126. US Pat. #1,871,020 issued Aug. 9, 1932). I think that there was a Craftsman that looked like this, but will need to go look at it to be sure. Nice find!
Any time that you wish to sell, PM me.