About all I can do is guess. 6 holes is used on nothing larger than a school bus and school buses are sometimes built with disc rear brakes. The numbers may have been stamped by the chassis manufacturer. International is big in medium duty like school buses, but I don't think these are international numbers. However, it really doesn't make a whole lot of difference where it came from. If parts are still available, Euclid would have them.
http://www.arvinmeritor.com/products/aftermarket/cvahydraulicbrakes.asp Most heavy truck parts distributors handle Euclid. Their catalogs have good pictures. I think Webb makes the rotors only. Ryder has an online cataloge, but its pretty tedious to go through it, but having 6 holes would eliminate a lot. I call people like Ogburn Brake and San Antonio Brake and Clutch and let them do the looking. I have about a 10 year old Euclid Brake catolog.
