Well the gears are as strong as each other, on early ASU type boxes the transfer box being made of cast iron will be stronger, as possibly will the transfer gears themselves.
As it weighs about 50 odd kilos the postage charges will be horrendous! depending when you want it for there may be a chance I can get it to London,
Mark (slateford) is coming over here from Edinburgh in his Rallye Via Dover/Dunkirk on Oct 23 & will be returning on Wed the 31st oct and he will be driving the M25 anticlockwise up to the M1 so possibly you could meet up somewhere?