After much gnashing of teeth, the overdrive is on. The input gear on the inside of the new coupling just would not mate with the female counterpart in the inside of the overdrive gear. The helical output gear and the layshaft gear slotted together just fine.
In order for the output gear on the overdrive and layshaft gear to mesh, the main and transfer box need to be in neutral…. this didn’t help. With the weight of the overdrive loading the surface of the coupling, the whole thing would retate, thus, not letting the input gears align (as it just kept turning) With either of the gearboxes in gear, nothing rotates.
In the end, I put the overdrive in gear so I could rotate the overdrive case and output gear at the same time. With a cold chisel “jammed” between the oil thrower and the lock ring for the needle bearing on the coupling (to stop it rotating) I managed to get some purchase on the input gear and the unit slipped on… a tiny bit. The overdrive had to be tapped home with a soft faced mallet. It’s a good fit and i hope never to have to remove it.
As with many things in life… finishing one job leaves you with another job to do to finish things off properly. In this case, it’s the extraction of the 4mm Allen Key (supplied with the kit) from the sump of the transfer case !