This is some great information! I already found that thread and read through it, but wasn't able to spot the differences myself. I wonder if it would be possible to source parts for the missing pieces, I'll have to look around for that. Thanks for the help!
UPDATE on the machine, I seem to have been able to fix the thread from breaking. I will to try to explain, but to be honest I had outside help and have trouble grasping the situation myself. The clutch motor had a perilex plug (not sure why). I changed this to a standard 16 amp high current plug. I was unsure about what the effect would be on the machine but figured I'd have to make it work anyhow, since I don't have a perilex wall plug. I kept working with the machine this way, but realized that I should've checked way earlier if we attached the new groups the right way. Yesterday we switched two of the groups and voila, the machine was stichting!
Now as you can see, while it is sticthing the lower thread tension is too low. So I went to adjust it. Interestingly the hook shuttle that is in my machine is also not the original (or the 27 subclass had a different one by design.)
The original manual shows screw 47, that has to be loosened before screw 48 can be adjusted to increase or decrease tension.
The manual: My shuttle:
Everything seems to be going well thus far, sadly as I went to adjust the screw it broke 😔. Maybe I used to much force or it was just because of old age, but I had a small heart attack when it happened...
So if anyone has any idea where to source replacement for that specific screw or just the shuttle, I would love to know!