yep, the GC perch's through hole measures 20mm, the shaft measures 22mm. Did GC change this maybe?
Like Dutch, I'll be making a spacer- with a larger opening so the step down on the shaft (from 22mm to 20mm) will be resting on the mount. It will also provide a nice surface for the spring perch to rest on. It's not the cleanest solution...I might just get rid of the gc perch altogether and merge it with the spacer, one piece aluminum.
Crude drawing (upside down, just the spacer):
