Well, looks like the spare engine is going to come into play! Broken piston ring parts (some) were in the sump but not all!. The starter gear (driven one) obviously caught some of the shrapnel and that has caused damage to the needle roller bearing and has also cracked the bearing housing in the gear. The primary chain is really worn and on the bench it is almost flat and the cam chain has made a bed for itself in the cam chain arm. Everything else looks OK including crank and shells (I will probably replace the shells) but I'll get everything degreased and the crankcases professionally cleaned and then a thorough inspection. Top end will be replaced and I'll decide what to do with the barrels once I have the other engine apart.
Oh and BTW, who ever put this all together did so with some sort of grey gasket cement that sets rock hard - needless to say it was a struggle getting things apart. It's all part of the learning curve!