I have the Gulbransen Service Manual which explains in detail and
drawings.  I use this roll mechanism for my Pistonola piano.  The heavy
cotton thread has been in use since 1973.  I recommend not to use fish
line as it is not sensitive enough.

The fishing pole gives no problems at all; clean it now and again,
and keep oil off the _friction_ wheels.  The adjustment loop is located
just before the steel wire enters behind the tracker bar; bend this in
or out to adjust the tension and sensing finger on the paper.

If you or anyone else requires the Gulbransen detail and drawings,
please let me know.

Regards
Steve Bentley