I've contemplated turning my 31-20 into a longarm set up but I'd have to have a plate fabricated to put a motor onto the machine. I recently sold my frame, which would have been able to handle the weight because of the need of the extra bedroom for the last 3 months and possibly in the future.
I don't know how hard it would be to figure out some kind of mounting plate or bracket for a motor, but I've not really had the mind power or energy to go much further with it.
I have guests coming today and it's dark and stormy, but I'll try to check the clearance space and hook assembly tomorrow.