I may have something missing here, or maybe not! does anything go between the washer and the bottom of the cross member? I set the mount just behind the cylinder head to push the box down onto the spring as it looked a bit close to the top of the tunnel, any thoughts on that?
The pin from the gearbox just passes through a rubber bush , parts book has no other part !
Once engine is in place on it’s mounts , and the gearbox mounting , you should adjust the bottom flanged washer up , to meet the rubber mounting . then lock it with the top flange and nut .
That’s by the book , but as we all know , slight variant’s are sometimes needed
I think I will pop a rubber donut in the gap, easy enough to reverse if it causes vibration etc, propshaft on, one carb on, may be running next week, may not!
Not sure home much it moves , would a spring , like on the other side be better 
Pleased your getting on well with it 
maybe, but not bearing on the rubber bush as that has no load on top and may pop out, will look and decide, down the shed now!
Hi From memory the correct sequence for the rear mounting pin is
Large metal washer spring then rubber bottom bush for the spring
This enables the rear of the gearbox to move a little and the hole in the pin is for securing the whole lot when removing the gearbox cross member
Brian
You should remove the pin, it was only used for transport from the factory.
At age the spring on the gearbox gets weak, and should be replaced.