Well on a first gen RX7 its easy as hell to change out the pinion/gear set..
First start off with a LSD which is not hard to find..Then decide what gears you want...
http://mazdatrix.com/g6.htm
This is why I love my first gen..Yeah a first gen..Like I said before Mods for my car are pretty cheap..and if I had the cash..I would drop a Ford 9