1970 Brake Distribution/Pressure Differential Switch

[sah62]

I could use some help identifying a pair of original brake pressure differential switches. I've attached a pair of pictures that I hope will better explain my question.

Which of these (if either) is a 3983040 brake pressure differential switch as used on a 1970 Camaro? The only difference I can see is that the cleaner one includes a plugged fluid port in a place where the dirty one is solid. The internal parts are identical. I have two like the dirty one that I bought as advertised for a 1970 Monte Carlo (which the parts catalog seems to group with Chevelles) and a 1970 Camaro. So, what are these? What other cars were they used on?

Thanks for any insights...

[L78 steve]

My 70 Nova has this set-up. I will snap a pic. when I get home Tues.

[L78 steve]

Pics. 70 Nova. This set-up is 70 only Nova and Camaro. It has the distribution block, frame valve and golf ball valve all together. My dist. block does not have the extra port that one of yours has.