Thought I'd take another stab at this - bought this bolt-on quick-disconnect system last year from Advanced Autosports for the Spec Miata build, but ended up using a different brand. System worked fine, installed one time but not taken to the track. It's a nice arrangement, hub should fit any Mazda. Includes adaptor to fit a Momo wheel. No welding required.
Paid $240 (see website), will sell for $150 + shipping.