You might find more information here:
http://www.supraforums.com/forum/sho...ing-wheel-hubs
At a glance it seemed to have decent info. I know I've seen this discussed on SM too. Other than finding someone who has their wheel off and can take measurements I don't think it's likely that youlll find a lot more info.... It's not something a lot of Supra owners worry about. You might also look for a thread on SM about swapping in newer Celica wheels, I think that had some fitment info.