I can help with part...
Pull the top shaft/gear/hydradrive, clean it up and drop it on ebay...If you want to keep it in tip top shape, hit every old hobby shop and search ebay regularly, there are some hydradrive rebuild kits on there occasionally.
Purchase a B4 top shaft, slipper plates, slipper pads and spur gear, fits in the original stealth no problems.
For the original diff gear...I cannot help there, maybe someone else has a source.
--Joey --Venom Batteries & Chargers!!
Old School Racer & Vintage RC Car nut
RC10CE (X4),B2,B3,B4,B5, B5m, B6D - 10T,T2,T3,T4,T5M - B44.3
BRZ-444, RC10M, RC10L3 oval, L4 oval X 2