I don't know the respective lengths of the TR6 axles but I have a set laying around. One measurement would be fully compressed (axle that is) and the other would be fully extended but with bolting the old diff and arms up to the frame I don't know.
I will check my files and see if I can reverse engineer the lengths (I took a million measurements when getting my axles made). FWIW, if the hub and the differential flanges are the same, Kevin at Ocala can make the shaft portion any length. All he needs is the distance from the hub mounting flange to the differential flange and he can determine the rest from there.
Good luck,