They are listed in the 1970 catalog, ( The standard plastic ones... ), on the HO Trains Resource site for Bachmann Trains. I think they were actually manufactured by either Roco or Rivarossi, and distributed by both Bachmann and AHM. The Gem that I picked up has the same drive.

Thanks, that's where I saw the information about the N scale model.

Hi... at a train show in Southern California yesterday, I picked up a Brass F9 in HO Scale that has a vintage Bachmann 8 wheel drive mechanism for power. The box reads that it was made by Gem, and the unit appears to mimic the style of a vintage Bachmann F9 piece. It appears to be brand new, and runs quite well. The only information that I could find about it on line was that around 1970, Gem produced Brass shells for Bachmann N Scale drives, which seems close... I would guess. Does anyone have any information about this piece that they could share? Thanks, Stephen.