I can say on my 84 the proportioning valve is down at the front of the frame on the passenger side under the radiator.
If I get a new master cylinder with a p valve up at the mc then the old p valve would be redundant and to remove it would require you to bend new lines out to your wheels.
It's probably easier to just gut it and leave it in place.
I'm just trying to think this process through because I am preparing for a brake system upgrade on my truck.