i don't think it will work...
1) i don' have one to check but i think the mounting holes on the toe blocks for the TC3 differ from the holes for the TC4. i think the 4 has wider holes...
2) the rear TC3 bumper is held in by the toe block through 2 "standoff" type extrusions which the TC4 blocks don't have, so even if the holes lined up the bumper wouldnt be very secure without the extrusions to key to the bumper.
Associated // Reedy // Radiopost // XP Digital // Parma PSE // Integy