I think/fear you're right.
The problem for me now is, that I still think I have read, that the screws has to be there (to hold the moving lens part in place).

Bu unscrewing one at a time seems like one way to go...

I took ar couple of snaps of my other Cooke, so you can see the plate with the screws (this looks original) and the markings in the glass inside..

Thanks for your help so far..