The gearbox was a common small engine PTO reducer type with a 6:1 ratio. All I did was re machine the end of the original geared crankshaft from the engine the gearbox came off of to fit over the shaft of a 2 HP 1800 RPM 120 VDC PM motor from a old electric floor polisher.
From there I just made an adapter alignment plate that allowed me to bolt the gearbox directly to the motor face and frame.
Given that the gearbox came off of a 12 HP Kohler gas engine it was plenty strong enough to work as a gear up system for the power levels I was working with. The gearbox was smooth and quiet plus being ran at a substantially reduced load I changed the oil in it from 80W90 gear lube to regular automatic transmission fluid which cut down on the internal power loss.
If you are thinking of going with a basic gearbox system this is about as simple and efficient as you will get using off the shelf parts and minimal machining work and non application specific parts.
This type of gearbox can be found just by doing a general search for these.
"Gear Reduction Engine"
https://www.ebay.com/sch/i.html?_od...70.l1313&_nkw=gear++reduction+engine&_sacat=0 "
or
"Smalll Engine Gearbox"
https://www.ebay.com/sch/i.html?_od...570.l1313&_nkw=small+engine+gearbox+&_sacat=0
They come in a number of different sizes from around 3 HP to 20+.
New they can run up to around $600 for the bigger aluminum ones but used cast iron ones like mine can get down to less than $40. However they come in two styles. One is a universal fit type that just slides over the engine crankshaft and the other are like mine that have the gear machined onto the crankshaft.
Lastly if you have a local scrap yard the odds are they will have a few of these around in their aluminum scrap section where they have all of the small aluminum lawn and garden engines. They are a very common small engine option that rarely ever wears out. With that route you may get the whole gearbox and related parts for less than $10.