I hate to admit this and will deny I said it if cornered, but if I had a back clamp machine that was going to be used - a lot, I'd hunt down a side clamp presser foot bar and exchange them. Very easy to do and it doesn't harm the machine one iota. My #1 and #2 66 red eye treadles were both converted to low shank long before I got them. Both came with attachments too. My one and only back clamp 66-1 came with nothing. Coincidentally I already had a set of feet for it. It will stay original as an example.
Joe