Thanks!
Obviously it's been a while since I updated this thread, but the crawler is now running AX-10 axles front and rear with an Airtronics 780 steering servo. The front diff gears are the hardened ones for the HPI MT2 (same ratio as stock) and the rear diff ring gear is stock, while the rear diff pinion gear is from a Wheely King.
These diff pinion gears look like this:
http://www3.towerhobbies.com/cgi-bin...4&I=LXJYM2&P=K
There is a hole in the diff pinion gear for a screw pin to go through it, just like you will find on the Maxx/Revo/Savage/Rustler/etc. The shaft diameter is 5mm.
Now see here:
http://www3.towerhobbies.com/cgi-bin...?&I=LXDDT2&P=7
That T-Maxx transmission output yoke has a 5mm inner diameter, as you will find here:
http://www.traxxas.com/PDF-Library/4910-08_tranny.pdf
The yoke is made to fit shafts with flats on them, so you have to drill out the yoke with a 5mm drill bit to make sure it will fit onto a 5mm round shaft.
Then you can use a regular Maxx driveshaft (4951X if my memory serves correctly).
As for the transmission, you can use the same yokes, but you'll have to shave down the end so it won't interfere with the transmission case.