Here's a more detailed story of how to attach the planetary gear to these RigidRc axles.
First I chance the drive shafts for longer ones that I made:
After that I install the new axle housing ends, those are tight fit over housing and kept in place with two M2 screws:
Then it was time to install the planetary gear to the adapter plate with 4 M2 screws:
Then the planetary assembly will attach to the axle housing ends with 15 M2 screws
There are rims that attach straight to the planetary gears, but the one I'm using are bigger, so I had to make new hubs over them.
And finally the the hub cap in place.
The Rigidrc axle are pretty nice and strong, but I strongly advise to put them in pieces before use.
The four screws that hold the differential housing together were more or less loose in all my axles. Put some thread lock there and they will keep tight.