Proportioning valve

[Mattax]

I'd like to know this as well.

Do the mid 70 distribution block/brake warning switch look visibly different then the proportioning valve/brake warning switch?

Yes

Ok, did some more digging. First picture is a drum/drum distribution valve with brake warning switch.

Second picture is a disc/drum proportioning valve with brake warning light switch.

View attachment 1715691926

View attachment 1715691928

Looks correct.

For future ref. the Imperial Club has many of the Chrysler Master Tech Pamphlets.
Master Technician Service Conference - Chrysler's Training for Mechanics

This page illustrates the disc brake system valves for '72
page 13 of Book 72-4 Disc Brake Service Roundup
Notice the trucks still had a seperate proportioning valve and distribution block (aka safety switch)