Firstly, i decided to build a new lower hull from my parts collection. 
Nothing really exciting here, just your standard Tamiya lower hull build from the reissue static Leopard/Gepard kits.

In that last pic you can see the gearbox adapter plate.
The old gearbox will not be going into this new hull. I have used a Tamiya King Tiger gearbox with the adapter plate.

I will be re-using the road wheels from the original lower hull. The rubber has degraded severely though so fresh rubber all round.