A quick round up of engine photos now that it is out and can be examined in detail. Some parts of it a pretty corroded. (click on photos to enlarge).
Very bad corrosion on the rear top part of the engine casing.
Quite a bit of corrosion on the front as well. I hope this comes off.
Here's the pesky shaft drive coupling.
Oh and this was what I hacksawed off to get the engine out of the frame. Now I can see there is a cross headed screw holding the assembly onto the head. It was too dark to see this the other night.