I had asked this some time ago, but I'm still not 100% sure -- I have a Riccar (Tacony) and from the plate up to the screw is less than 3/4", so I'm sure it could be considered a short shank. But the feet come off with a lever (snap on?), not the screw. So would I use a walking foot for a short shank or do they make snap on?

I have not seen any walking feet that snap on. I've seen several different ones and they screw in where the ankle piece goes - this is the part that the snap on attaches to. I don't know about your particular machine, this is a general comment on what I've seen.

So what happens is you unscrew the ankle, screw on the walking foot, making sure that the right side lever (not sure of the name) goes over the screw that tightens the needle.

Thanks - I think I finally got it.

Make sure the screw that holds it on is long enough. I got a walking foot for my machine and the regular screw was to short.