Here's what I have figured out so far (mostly based on my conclusions so far and subject to change).
For General Electric:
731 - 600 volt "wheelbarrow" mount - standard gauge only ALCO S1, S2, S3, S4, RS1
733 traction motors are 300 volt, self ventilating, parallel mount through a double reduction gearbox, and are about 200 hp maximum. The double reduction gearboxes appear to have been available in at least two gearings - about 20 mph or 35 mph maximum. There are suitable for 36" gauge because the gearcases allow the motors to be mounted so they extend to the side beyond and outside of the wheels.
747 traction motors are 600 volt, self ventilating, right angle mount and are about 200 hp (maybe more). The gearing appears to be about 30-35 mph. The gearcase appears to limited them to 36" gauge, but other gearcase designs might have allowed narrower gauges. Also used in cranes.
748 - 600 volt "wheelbarrow" mount standard gauge only GE 70 and 95 ton
752 - 600 volt "wheelbarrow" mount standard gauge only GE U25B+ (ALCOs?)
761 - not sure but appear to be 600 volt, force ventilated, parallel mount, different gearcase (double reduction?). Might be a version that is also wheelbarrow mount for 36"+ gauge (or another model?)
763 - replacement for 733?
I have not been able to determine yet if GE offered wheelbarrow mount traction motors specifically for meter and/or 42" gauge. There are also a few smaller motors (ie 23 ton 24" gauge)
Westinghouse: 928A wheelbarrow mount 600(?) volt 100+ hp for 36"+ gauge (Porter s/n 8096 USG/Huck/SVRR/Loop 1203) also used in cranes
EMD: D29 (and possibly D31) are 600 volt wheelbarrow mount force ventilated for meter gauge plus. EMD export models with these get the U designation added to their model (for Universal traction motor)
EMD 36" gauge units for Columbia - unknown model traction motors - from outside supplier?
