For the collective expertise here.....
Mk2 carrier last run 10 years back, but was a good runner. (smoked a little)
We got it non-running. Did the usual stuff to check it prior to spinning the engine.
Added a new battery and was checking the spark and was very weak.
Pulled the distributor. - Original 'Diver's Helmet style.
put a new coil in it and cleaned the contacts and all the stuff you do to a distributor and went to put it back in.
Here is the problem...

When it is seated, the tab does not seem to reach the slot on the cam shaft. with the round caps off, you can spin the shaft to get the tab to line up, but Joe says it keeps spinning and does not engage.
We have tried to fit just the shaft from a spares box and also with the end cap and the shaft.
I am beggared to think the shaft could travel out of position like that!!
Since I don't have personal confirmation the distributor wasn't tinkered with by the previous owner, I don't know if something went wrong with the cam and that was the reason for not still being a runner.
Or..... Joe just hasn't gotten the distributor housing fully seated.
Has anyone run into this before? Is there some sage "oh, by the way..." about fitting the diver's helmet distributor that we are missing?
Thanks all.
Joe thinks the cam shaft has shifted rearwards somehow.