ok i lied before. I didnt cut anything off the primary chassis.
I just cut the secondary so the tab from the primary would rest on top of the shorter wall of the secondary part after being cut.
then i superglued them together, it took a few tries to get the two peices so they would be level with each other.
then I ran wires from the back motor to the front motor and *voom*
sorry, can't explain it very well today.
Note: these were clone cars from KB.
blurry images to follow...