I just saw that Fred posted that the F104 axle and diff assembly MAY be used on both the F104 and the F103 as it is a hop up option offered for both chassis.
The aluminum F104 motor pod MAY NOT be used on the F103, only the F103 parts may be used.
Now I'm really interested in finding out if there is an aluminum left side gearbox from Tamiya for the F103!
Anyone?