The Stovebolt Site Forums The Shop Area Driveline rear brakes

This is kinda a stab in the dark since all you can find is a "J", but here's what I can offer in hopes it helps. Research through GM resources indicates for 1973 that there were two primary 10-Bolt (8.5") rear axles (ratios 2.73 to 1 and 3.08 to 1) identified with the first letter J used on selected GM X-body cars (Chevy Nova, Pontiac Ventura and Oldsmobile Omega). This 10-Bolt is virtually the same as the Camaro (F-Body) rear axle which did not use a "J" as an identifier, so easy to mistake one from the other.

On what may be the best note on your brakes for this axle, the GM X-Bodies and F-Bodies share the same basic brake components. Brake shoes and wheel cylinders specifically are interchangeable, so the new parts you have (purchased for a '73 Camaro) should work just fine on your axle.

I can't say anything on trying to find exact matches for the old shoes/cylinders in your first picture above. They look different than the standard shoes and cylinders I'm used to work with. Honestly, I think you should be fine installing the new cylinders and shoes you've purchased.

Below is just some resource reference info to demonstrate some of the information above and the different models using the same brake parts.