So your truck had horrible brakes when it was new? My experience with 4 wheel drums was good brakes unless they got hot from frequent use, or they got out of adjustment.I got rid of mine because my truck originally came with drum brakes all around. I would have to open the door and drag my foot to help stop it.
My goal, when I got my truck back in December '73, was to fix the horrible brakes.
It took me about 12 years to convert to disc's on the front. It took me another 8 years after that to put disc on the rear.
I did a lot of things between those years to improve the braking.
I got rid of the stock proportioning valve around the rear disc conversion. It just made adjusting the front to the rears do much easier with a adjustable one.
You already have better brakes than I did stock. You should be fine with what you have.
As mentioned above... put fresh fluid all the way through your system. Brake fluid will get water in it. Water will destroy lots of things.
Thanks Dean. I'll grab some DOT 3 tomorrow.l,d soak it in a [ use a coffee can or what ever] with brake fluid and then blow it out with compressed air
use a tooth brush or whatever to clean it up / l would NOT take it apart unless you have replacement parts handy [ o-rings and seals ] like what was said before its a NON wear item = if it aint broke dont fix it