New Project, D Grader

Her there,
Picked up a little Allis D grader over the weekend. I'd kind of had my eye on them for awhile and this one came up with some options I was looking for. Its S/N is in the 4000's, its got hydraulic tilt steering, the hydraulic circle rotation, and after market power assist steering. Needs some odds and ends but nothing that can't be overcome.
The biggest thing I need to find is a replacement orbit motor for the circle rotation. I'm doubting and OEM one is going to be available, but I'd think a generic motor wouldn't be impossible to find and adapt.
Does anyone have any idea how I'd go about looking up some general specs to size one?
Looking like it will be a fun project to mess around with
Here's a picture

Nice looking D grader. It doesn't look as if it ever got used much. The special model with all the options. Does it have the serial number plate? If you have the serial number I can tell you the model year. The belt driven pump plus standard threaded pipe fittings to some of the cylinders tells me that the system it not a high pressure hydraulic system so a hydraulic motor that required high pressure would not work that well. From the blow up in my parts book they look like a basic gear hydraulic pump but working in reverse. There doesn't seem to be much to them. Have you considered trying to repair the existing unit?

Hey Don, Thanks. It needs some TLC but it seems to be solid enough. The S/N is d-4834
DiyDave, thanks for the tip, I'll have to check that out
I talked to a guy who has worked on these older rigs quite a bit and he had said from his experience the parts are getting difficult to find and by the time you mess around with rebuilding and orbit motor you could of bought a new one off the shelf. I need to do some trouble shooting though and make sure its not a pressure issue.
B26240, I'm only about an hour from Grand Rapids, I'll have to look those guys up

That hydraulic motor is not an orbit motor. It a gear type the same as a gear type hydraulic pump. It has two gears, a couple of 'O' rings, a couple of gaskets, a couple of wear plates and a seal assembly on the output shaft. Engine parts are easy to find but transmission/axle parts would be hard to find.