So sadly, this project has come to an end. Upon disassembling the supposed "good" engine, I found quite a bit of shavings in the oil pan. I started disassembling the engine to find the place the shavings originated from (seemed to be aluminium, so most likely a spun bearing hole), but I rarely have time these days and even less space to work in. The frame is standing outside, and falls over every other day. They now also removed the hedge it was standing behind, and is now in full view from the street, an eyesore to be sure! Its a tough decision, but I think it is the wisest for now.
Yesterday I disassembled the frame in the quickest way possible, i.e. using the sawzall. 12 seconds!
So now I'm wondering, does anybody want any parts? I'm keeping the 40A alternator, carb set, rear shock (Hyperpro) and front forks (hopefully with hyperpro springs inside), for a running and driving ST1100 I hope to buy in the not so distant future. I don't want any money for it, if you cover postage I will (try) sending it your way.