The prop valves should be the same for all GM vehicles. When you are looking find one that includes the mounting bracket and the little pre-bent lines that connect to your MC. I got mine with an entire disc conversion kit from POC. The booster, MC and prop valve came from CPP. Mine looks just like the one 64 shortbox posted. Just make sure it is for disc/drum. The one I linked below has everything (bracket & lines) including the plug to put in the brake sensor port to keep the valve centered when bleeding. The bracket should mount to the mc/booster bolt on the drivers side and them bolt to the prop valve itself. The lines will also hold it in place. Then you will connect 2 3/16 lines to the front of the prop valve to the right and left front discs. The port on the back will be for connecting the 1/4 line to the rear drums.
https://www.jegs.com/i/JEGS/555/631302/10002/-1