Help with Brake Drum Part Number

[Joe P]

I have a 66 K20 and can't to find a part number for the rear drum. It's an HO72 with 13 x 2.5 inch brakes, 8 lug. This Eaton housing is the wider version to accommodate single rear wheels. I do have a set of 13 inch drums on my dually Eaton but that housing is an inch or two more narrow and the drums are different. I have piled through the parts books, this website and the other one, and paid an online visit to suppliers. All drums listed are 11, 12 or 14 inch, no 13's. I wish to keep the original brakes on the truck. Drum brakes work well for me, especially in the rear, so no disc conversion. The old drums I have are not salvageable and any markings that were on them have disappeared with time and weathering. Is there anyone who has been down this dark alley that can offer a flashlight in the form of a part number? Appreciate your time and courtesy!

Joe