Thanks PC! It only took 12 replies to finally get some useful information!

I will offer the additional "opinion" that if you could find a D32 industrial/marine generator and motor, perhaps in the Houston area as they were widely used in land drilling rigs, it would be a much easier set of equipment to use than trying to convert a pair of D4D generators. There is a lot of design and machining work necessary to make pedastel bearings to adapt the D4D to be a propulsion motor, and you don't know if the machine is really electrically suitable for the application unless you could find an EMD rotating electrical equipment designer who was familiar with them.

PC

OK thanks. I'll start looking into the D32 and see what I come up with.

I have a distant memory from an electrical engineering class more years ago than I care to remember that DC motors and generators are somewhat interchangeable. However the device had been optimized (lamination design?) for the purpose. Therefore a purpose designed generator was more efficient than a motor and vice versa. For the use discussed here this shouldn't make much difference.