The gearbox bearing that I thought was shot turned out to be OK - perhaps something got in there while I was taking it apart, anyway "washed" it out with some WD40 and it feels OK.
I heated both bearings up again with the hot air gun and they dropped onto the crank and gearbox shafts tapped them home for good measure.
All set for re assembly once I have the small rubber seal that goes between the cases - hopefully some time during the week.
The main bearing had a few spots of loctite on it, which made it a little more difficult to get out.
It may be that I did not have the cases hot enough when dismantling, but I have never done one of these before so it is also a learning excercise.
On re assembly I will make sure that the case is hotter, so hopefully will easily drop over the bearings.
Been looking at the MZ Factory video on You Tube, and placing the bearings onto the crank and gearbox and heating the cases seems to be the way they do it.