I may not have mentioned it but last year, whilst cleaning up my workshop I knocked off the shelf the casings for the 1st engine rebuild – aarrgghh! Anyway what we did was to fill the hole with plaster of Paris (actually it was a moulding material used by dental technicians) and then clamped the timing cover on and held all the bits together. The 3 bits were chamfered first so that the welder could weld up the aluminium better. The main problem in welding old castings is that they can be porous and contain oil. This makes welding a nightmare. The guy I used is very good and the end result looks good. I will post a photo of the casings later now that they are vapour blasted.
The above photos are not in order, but they will give you an idea of waht was entailed. The red paint was an accident at the same time!! (I had a bad day!)