[RichardJ]

>>proportioning valve for the 73-87 was located on the front crossmember. Since mine is located below the MC <<

If you are referring to the item visible in your first picture, that isn't a proportioning valve. It isn't any kind of valve. It's a switch. That's all it is. It is there to turn ON the dash brake light indicator. If there is a hydraulic brake failure in either the front or rear brake system, that switch will turn ON the dash indicator light, if you have one. That same indicator lamp would be used for youe E-brake light.

Without a proportioning valve in the system, you should be able to lock-up the rear brakes with ease. On a wet road, you should have a hard time keeping from locking up the rears. If you don't have that problem, your front disc brakes are not working properly.


>> proportioning valve for the 73-87 was located on the front crossmember.<<

That isn't just a proportioning valve. It has the brake light switch, plus a metering valve for the front disc brakes, plus a proportioning valve for the rear drum brakes. It is called a Combination Valve because it combines all three of those functions into one unit.