I replaced the chain in an OM603 and M103 by myself without special tools other than zip ties so it can be done. I have a big 'learning' account so I'm not afraid to mess up

If I understand this saga, the chain is still apart and the tensioner is off. If so, I don't trust any of the alignment readings. The reading I'd trust most would be taken by holding the cam sprocket steady and turning the crank sprocket CW as far as it will go.

From what I remember rolling in a new chain is not a 'linear' process. The IP or vacuum pump will cause that sprocket to act like a capacitor. You'll turn the crank seemingly forever with no corresponding movement of the cam then 6" of chain will get sucked in. Freaky! However, it is precisely this behavior that lets you manage the task by yourself. Once you figure out the timing, no pun intended, you'll realize that you don't need constant tension on the new chain (I have it pull itself out of a can of oil) or the old chain (I let is dangle out towards the water pump).

If you've ever had the vacuum pump off, you'll know there's no way the chain is coming off the timer. When I pulled the IP off the SDL I left the timer in the chain. I put some zip ties for good measure. It's a chore to get the timer off the chain. You have to slip a shield between the timer and the chain as you slacken the chain from cam. Some line the cavity with grease so the chain sticks to the walls.

My 2 cents - there's no way the chain came off the crank or IP timer. If you're sure the chain didn't come off the cam, I'm sure cam timing is how it was before your neighbor left for his trip. 2 cents doesn't fix many bent valves :/

Sixto
93 300SD