Yes, Manfred, you will only be able to adjust the timing by one tooth increments, but the S6/T6 motors are only in a soft state of tune, so it is not imperative that the timing is spot on. Always opt for over advanced rather than retarded, as you can then play with the advance/retard lever to find the 'sweet spot'. Also, bear in mind that we now use fuel that is nothing like that available in 1930, so the engine is likely to run sweetest with a different amount of ignition advance to that specified in the handbook.
As far as I am aware, there is no spring inside the generator coupling sleeve.
Regards,
Eddie.