Using modern internals such as TD2/4 ball-diff or gear-diff with a modified PA12 printed gearbox. Even older TA-06 diffs can be used with some shims. The benefit are 12 instead of 10 differential balls and larger outdrive bearings. The original Dyna diff is really strong, but this mod can take a little extra torque. But the best of all, spare parts are still available.
The mainshaft is designed to take modern slipper clutch such as TD2/4/DN01. Many spur gears can be used, even wider ones. Original mainshafts can be modified as well but since they are very rare it might be better to keep them as original.