Ok .. I got the drive wheels done...ish I used the hole in the nut trick that RC Modder uses in his Bruder conversions and it seems to work pretty well. I drilled a roughly 2.5mm hole on the flat side of the nut and tapped it for a 3mm set screw.
Now the axle holes in the wheels are to big ...of course so I bought a set of copper tubing that all the pieces telescope into each other and I took the piece I needed to get the correct inside diameter to match the turned down axle shaft on the Tamiya gear box and then used the next size up to get an outside diameter to match the Bruder wheel.
The fit was snug but not tight so I used some JB weld on each piece and the inside of the wheel and let it set up overnight....it seems like it's on solid piece.
The nut is 5/16 and it screws onto the wheel, it's a tight fit and actually cuts some shallow threads in the plastic. once I had it flush I drilled a 2.5mm hole using my threaded nut as a guide thru one side of my wheel then ran my 3mm tap thru it again to thread everything. I left a lot of burrs inside the wheel but a little work with a tiny round file and it as all cleaned up. I used a long set screw and put a flat side on the axle shaft and it tightens down really well.
Now time to get the wheels ready for the 9 drive pins you need to add so the tracks to grab. Here I just marked where I wanted the hols, Bruder uses every other notch in the track so you drill accordingly....
This is my 2x4 block with a hole drilled in it deep enough to let the wheel sit flat while I drilled the holes..
I just need to drill these out and figure out some pins....