After 5 years of searching, a friend pulled through! I have an SP5 (ball) cartridge and as a bonus what I am told is a VSS Vintorez magazine!
No more guess work. I am measuring the cartridge so I can make a diagram, then I'll make a reamer. I may actually submit this to a reamer mfr just so they have it on their list. Funds are kind of tight right now so that will be later down the road.
More pics to follow.