Most of the "proportioning valves" I see advertised are more properly called combination valves as they have metering valve, proportioning valve and failure warning switch all in one unit. I assume that's what you have.
I don't have any additional RPVs in my setup. I have Camaro front disc brakes, Camaro rear drum brakes, Camaro combination valve and Camaro master cylinder. So it's all matched like GM designed and the brakes work great. (note that I have a 1/2 ton)
I see people on this forum adding RPVs. I assume that they have to do this because they are not using matched components and the rear brakes are not doing their share of the work.
You will have to do some testing.
