Given my experience over the years with aftermarket brake parts in older vehicles, I'd focus on sticking close to GM parts. Your truck already has some serious rear brakes, and I'm not sure you'd see a heck of a lot of improvement even with a $700 aftermarket disc setup. Same goes for the front rotors and calipers.
I'd start with new name-brand calipers and drums, and consider high quality pads and shoes like Wagner Severe Duty. If you try to get by with turning the rear drums, their inner diameters will not fit flush to a new set of shoes, so you'll need to go with new drums (or find a shop that can still "arc in" shoes). it's very common for someone to get their drums turned and install new shoes, only to discover the brakes are worse than they were before, because only the center 1/3 of the new shoes are actually contacting the turned drums.
As an option for the front, Wilwood makes a D52 replacement caliper kit for 84 C20 that works with stock rotors, but they don't show anything for a C2500. I don't know if those models used the same calipers & pads or not. Anyway, their 2-piston calipers put a more evenly distributed clamping force on the pads, and their BP-10 pads work pretty well, or at least they did on my manual brake 55 Chevy sedan.
And don't forget to flush the system with fresh DOT 3 fluid.
Edit: According to the spec sheet below, front brakes are, in fact, the same for C20, C2500, and C2500 Crew Cab. However, rear drum brakes are larger at 13" x 2.5" on C2500 and C2500 Crew Cab.
https://www.gmheritagecenter.com/do...its/Chevrolet-Trucks/1984-Chevrolet-Truck.pdf
On a final note (finally). Whether you use a vacuum booster or hydroboost, it all starts with the quality and condition of the friction components. Otherwise, adding boost will be like putting lipstick on a pig.
