After a few tantrums I have successfully install Marcus53's two motor/gear system with the freewheeling connection. I had to modify the design a tad but am now very happy with the result.
I could not make the M motor on the rear diff skip proof, so I put an L motor in the cab using the sprocket and shaft from the steering assembly and hitched that to the Center diff.
A servo motor on the front assembly replaces all factory steering.
I used slightly different gear ratios to get better speed, I found Marcus' painfully slow.
A great result that I'm happy with at the end of the day.
Marcus, your a genius! Cheers!
Pics to come.