Motors
I chose the Lynxmotion GHM-12 for this conversion. A detailed spec. sheet in pdf can be seen here.
Start by grinding the flat on the shaft longer.
Remove any plastic that will stop the motor mounting against the side of the hull. Note how I have left as much plastic as possible on the side of the hull.
Drill through the existing hole to allow the motor bearing to be a snug fit in the side of the hull.
Make up a plate from 2mm platic card and stick it to the side of the hull.
This will help to support the motor and improve the strength of the hull.
Drill the motor mounting screw holes from the outside of the hull.
Here is a template to use for drilling the holes for the motor.
MAKE SURE it's the correct size before you use it, you can print it out and punch the holes through.
Three holes drilled.
This is what is should look like when fitted.
This is what it looks like from the inside, with motor suppression capacitors fitted to the motor.
Side View
Note The side of the halftrack is not vertical and you need to put a couple of washers between the top of the motor and the side of the hull to make the motor shaft horizontal.
Fit them on the upper mounting screw.