The pinion needs shimming to mesh properly and you have to use a through pin to secure the drive cup to the pinion shaft but it's very simple to do. No mods. are needed to the diff. housing as FTX uses the same bearings as Axial and with just a little shimming everything drops right in.
What I mean about a through pin is that the Axial pinion has a hole through its' shaft it instead of the flat surface FTX uses for a grub screw. It works just the same as how the FTX rear drive shaft attaches to the out drive from the gear box.
I trashed my stock ring/pinion whenever my buggy landed on it's nose from higher than two feet in the air, the chassis flexes soo much that the front drive shaft gets pushed into the pinion which then drives it right into the ring gear and smashes the teeth on both. I've not worn out, or stripped a single stock ring/pinion set but I've smashed a few.
I'm making a chassis brace to stop the pinion from smashing into the ring gear, when that's sorted out I'll run the new Axial gear set and report to you guys how everything works.
The best thing about Axial gears (or the aftermarket gears for Axial vehicles) is the option for underdrive, or overdrive gear sets. I have the overdrive gears for the front of my Outlaw to help it climb hills but the option is there to tune your vehicles gearing by running over, or underdrive gears to get the gearing you want if you can't get the spur/pinion combo to suit your needs.
I'll make a new thread with pictures of the Axial install since it applies to every FTX vehicle running the same differential as the Outlaw.