[caffel]

The details are on Chief Delphi elsewhere (some from 2002).
Summary:
Older motor has 9 teeth, odd Diametral Pitch (36) only matched by the 'coppery cluster gear' in the jack.
This gear has 16 and 44 teeth.
The next gear in the drivetrain has 80 teeth.
Advice per our experience & Joe's advice above: Use the intermediate shaft that came with the plastic gearbox. Keeping the clutch as well. Lengthen this this 3/8" shaft and extend it through the case and use it as the output.
This results in a 225 RPM free speed.
Discard the old final output shaft and the last stage of reduction.
Prior to this, we made a new shaft (for the 80 tooth gear) and cover and had failures due either to misalignment or overloading (as Joe predicted). Of our two gearboxes that we made this way, one has been fine through a lot of use and the second failed twice.
CA