Thank you for puting me on the right track.
I think I am almost there. Virtualdub, Avisynth, ffinputfilter, ... lots of processing and gigantic files. I never thought it would be so cumbersome.
I was able to recover a 45 year old 8mm film using an old and slightly broken film projector. The projector would only display the film decently if put in reverse, i.e. running backwards from end to start. I then recorded this projection using my camera (Nikon D800). This method worked wonderfully w...