my mate has a mark 3 escort s1` replica.weve put a 1.6 carb engine in.but used standard 4 speed 1.1 gearbox.gearbox has now gone.i know mark 4 gearboxes wont fit.do mark 5 or 6 gearboxes fit as thats wot ive been told.because its going to be really hard to find a good box out of a mark 3.can anyone help please?