Update:
I decided to use the motor and planetary gears from an old cordless screw driver to power the half track. I took an old hex bit and heated it till it was almost white hot with a propane torch and then let it cool slowly removeing the tempering(hardnessd) then chucked it in a drill and turned down one end to accept a section of brass tubing, Here is a pic of the finished parts before assembling

next I remove some of the cross braceing on the drive axel section, and cut a small section out the center to allow the differential be at the right height to mat up with the drive axel. I also cut a small square section in the floor to allow for the bottom of the differential. Here is a pic of the drive train in place.

Next I cut out a section in the bottom of the firewall for clearance of the differential. Next I will remove a section of the sub-floor for the differential. It will be hidden easily inside the bell howseing and by the trany cover howseing. Here are 2 pics from either side of the firewall
