After a suggestion from a LFP member and some head scratching on my own, I made a gasket out of an old mouse pad and inserted it between the body and the cone. This gives me a 5mm of extension, which provides both infinity focusing and a sub 2m close focus. The rear element of the SA still bumps into the inside of the helecoid, but helecoid is now securely screwed into the cone. There goes my opportunity to buy a new lens.

I also found that a 21mm finder for a 35mm rangefinder is a very close match for the angle of view for a 90mm @ 6x17. I need to figure out how to mount it to the Gaoersi and my vertical masks need to be reconsidered (post-its at the moment).