I have a similar setup in my '75 GMC k25, and I'm working on my upgrades.
The most significant OEM weakness of these engines is the poor flowing cylinder heads. You can can change intakes, carbs, exhaust, cam and other items, but it will all be limited by the heads. If you want a more long term plan, it should include better cylinder heads.
Short term upgrades - 4 barrel manifold and carb, cam in the range of about 214 @ .050, headers and dual exhaust. You can usually pick up about 50 HP, but you may get even more increase because you have such a low performing carburetor.
Longer term plan - Vortec iron or aftermarket aluminum heads. Same 4 barrel manifold and carb, cam in the range up to about 218-220 @ .050, headers and dual exhaust. This package will get you about 100 HP if you don't change anything else. If you are willing to use lower gears and a high stall torque converter, you could use a more aggressive cam and get more horsepower.
Your truck is heavy, so you cannot use an high duration cam (for example, lift at 225-235 @ .050) and expect to have low end power with stock gears and converter.
I like roller cams, and I bought one myself, but it would add a lot to your expense. With a flat tappet cam you could reuse your rockers and pushrods, and just buy new cam and lifters. With a retrofit roller cam you have to buy the cam, lifters, new pushrods, new rockers (usually), and you need a cam button and new timing cover. The upside of using a roller is that it has lower wear, and can handle fast ramps and higher lift cams.
Bruce