I bought new metal differentials. If I’m not mistaken these are from Tamiya TT01 chasis. Fits well to the bulkheads and I only had to add adapters for bearings. Also designed the central gear. I got a metal attack gear with 0.8 module so I changed the central gear to fit too (56T). Unfortunately I didn’t make enough clearance so it was rubbing on the housing side and has welded eventually (2nd photo). Corrected this and fits good now. But I still need to fit the central drive shaft because ones I have are too long now.
Tt01 is a pretty common chassis so using parts from it wouldn’t be too bad! Did you print the adapters or is it metalwork? I wonder if the diff case could be easily adapted or suitable bearings that don’t need adapters could be sourced?