hi greg thats exactly what i have done ,,just home from work and its running great,,just need to hook up lights and fire boxfor isolating the motor from the track pickups...
First, replace the missing brush holder in the truck.
Next the easiest thing to do is carefully unsolder the motor wires and extend them. You need to be careful not to break the connection between the strip of brass that comes from the brushes and the small piece of brass that straddles the wall of the housing and brings the power to the 2 slots outboard of the motor, to allow the brass contacts in the chassis to pick up.
This way you only disconnect the motor leads and extend them into the chassis, and leave the track power pickup circuitry alone. This is the easiest way.