If you’re able to make a suitable 3mm thick spacer you can add an extra reduction stage to a 22mm brushed gearmotor for 64:1 reduction, or you can steal the ring gear from another 22mm gearmotor and thin it down to 6mm to stuff in two extra reduction stages for 256:1 (probably a bit slow).
I’m still experimenting with this in my beetle, and the advice above is probably better, but it seems promising so far - I’m running two motors modified like this in parallel and they come in at about 140g combined.
I’ve got some of the 37D motors, but I’ve been avoiding using them because it’s my drive pods rather than the lifter that are actuated, so I want to keep the ability to control them separately if possible to get them back in sync if (when) the belts slip.