Doncan,
Here is the link to the 5.12 r+p
http://www.mazdatrix.com/getprice.as...m=27-1100-1480
You will also need the long pinion from your 2nd gen, because the long pinion and the new 5.12 short pinion will be cut in half and welded back together to make the long nose 5.12 pinion .
While you have it apart, new bearings, disc's and seals.

Have fun, I know that I would not attempt this procedure.