I'm about to turbo my Miata, and one of the items sitting in my basement is a full 3" exhaust. In the rear of the car it gets routed up under the subframe brace, near where the stub/halfshaft flange is. Some people who have made 3" exhausts have had clearance issues with that flange and have gone to the later 96-up single piece halfshafts for clearance (no flange to hit stuff). My fabricator says I "should" have room with the way he built it, so hopefully I won't have to mess with it, but on the off chance I do end up having to switch to the one-piece shafts I can give you my '94 ones.
There ought to be people on the forums with open diffs sitting around. I can post a WTB ad on your behalf if you like. If you have any local Spec Miata racers check with them too as it's not unheard of for them to accumulate parts cars. <img src="/forums/images/graemlins/lol.gif" alt="" />
BTW when you get around to looking at that RX-7 diff, a 3.909 should have 43 teeth on the ring gear and 11 on the pinion. <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/smile.gif" alt="" />
Drivetrain swap stuff confuses the crap out of me, frankly. I have a few links saved so I don't have to use my brain remembering any of it. You've probably already seen these but I'll post them just in case.
http://www.solomiata.com/Drivetrain.htmlhttp://www.solomiata.com/RingandPinion.htmlhttp://miataturbo.wikidot.com/differentialhttp://mazdatrix.com/g5.htm
