Well, the answer is YES
You can remove & replace the gearbox, without removing the interment shaft.
The gearbox went on reasonable easy, to be honest. Little bit of thought& planning, an extra pair of hands
It alined up, both shafts first time
That was the good bit.
The rear engine Mount failed to line up, & we ran out of time to finish the job
The gearbox to rear mount bracket, caused problems, - just couldn’t remove in the car. So the engine Mount, needed to come off, this reviled a split engine Mount
, another job for the coming weeks, but as a ‘stop gap’, I’ve filled the whole engine Mount with mastic, to make it solid. Just the same as putting in the ‘up-grade’ inserts.
Kit
getting at the bearing bracket, behind the bends of the front pipe, looks a right pain 
