Not sure about Yale but Hyster and Clark stamp the numbers in the top of the frame on the RH side usually somewhere along the rear near the engine.
Call The Berns Company or M&M Forklift Salvage they may be able to help.
If all else fails, see if a standard dust cover will drive into the threaded area of the hub. If the unit has no data plate, and you plan to use it for business, watch out for OSHA. For private use, not a concern. Google Yale forklift on google images and search for a visually similar unit. I find a lot of items using this method.
Looks like an old Towmotor.
I'll try n see what I can find on Monday. Work parts at yale dealership n we have some old books on the shelf yet
