Thank you Carl
Michael I used the cover and shaft from the front diff box, the shaft pulls away from its connectors which joins it to the motor, you'll need to make a new shaft to join the 2 rear shafts together as they both have the same fixings so they will not slot together. Also you will need to have the 2 rear diff boxes offset to each other, ie one towards the left side of the axel and one to the right side so the gears are reversed because if you have them inline with each other they will rotate the opposite way to each other, one going forward and one reversing

this took a bit of head scratching to figure out when I first did it

I hope this makes sense if not let me know
Cheers, Lee.