I feel like I have to throw my two cents in here I'm not sure why. Here's a good example, I have a 2019 Buick regal TourX, it's my daily driver. Overseas you can get this car in a GS trim package which had big front brakes. The stopping distance between my car and the one with the big brakes I think is within feet. It's really no difference when it comes down to it. Once the wheels lock/abs kicks in the brakes can do no more. Were you benefit from the big brakes is heat dissipation. Yes I am simplifying this greatly, but if you can threshold brake over and over again you can put most cars into a situation where the brakes would fade and stop working. The bigger the brakes, the more you can do this without that happening. Larger tires too can decrease the change of the wheel locking under braking, so bugger brakes could be taken advantage of as the threshold for locking would be higher. So if the OP can lock up all four wheels with the stock brakes, The question begs to ask, do the brakes really need to be bigger? And if he can't, what is wrong with the stock brakes?
Now there are obvious reasons for an upgrade, the ones I mentioned being able to get on the brakes longer get them hotter, more stops from high speeds with less worry about fade. Possibly rebalancing the brakes putting more of the bias towards the front, because of the tendency for the rear to lock up with no weight can have added benefit. However with more the work being done by the front brakes if you rebias then, it then begs the question should you probably upgrade the front brakes?
From experience I have driven cars with horrible brakes, that shouldn't have horrible brakes. In the end it ends up being a poor quality of brake pad and rotor. Yes rotors alone can cause a brake system to work very poorly, I've experienced this on more than one occasion, once on my own car. My suggestion would be to properly stage zero the brake system on that truck. It's an iron duke truck, 90 horsepower on a good day when it was new so won't be breaking any speed records. Refresh the front pads and rotors, and the rear drums and shoes with a known good quality parts. Personally I've used centric on most drivers with no issues pads and rotors. They're very inexpensive, they're made by stop tech and they just work. You can also go with AC Delco dura stop stuff too. But be sure you do it properly, new wheel cylinders, new spring kit, if the calipers are super old it's not going to hurt to swap them out they're usually dirt cheap. The brake pedal on that car should be firm and it should stop well without any question is too is it actually going to stop. If the pedal is mushy and the brakes just don't feel great, there's a good chance you have a proportioning issue or a brake booster issue. I have seen brake boosters lately cause all kinds of very strange pedal problems that you would normally start poking at the hydraulic system to try and fix. Also very poor quality rotors can cause a brake pedal to feel strange as you're not getting the grip from the brakes with a normal pedal pressure so you have to push deeper into the pedal which can also feel strange. It's kind of a messed up cycle of crappiness.
As far as upgrading the front brakes to a two-piston caliper, I mean it can't hurt, but I don't see it increasing braking performance unless you have a larger tire and you can get on the brakes a lot harder before they lock. Then you might benefit from a two-piston caliper. But if the rotor is the same size, eh. For stock daily driver, a good stock brake setup should be fine. But if you're going to be changing the calipers anyway, and it'll be swapping all these parts out, pads rotors calipers, you have nothing to lose and it may not be a bad idea to upgrade if the price is comparable.
But to answer the OP question about doing disc in the rear, on a stock vehicle like that I go not so much. The advantages you won't have to adjust the rears anymore, the disadvantages you have to figure out how the parking brake is going to work. You can grab everything from one truck and bolt it on and your stock parking brake cables work great, then you get otherwise figure out how the parking brake cables will work. And in my experience, you can't beat a standard drum setup as a parking brake, versus the integral parking brake inside the rotor hat, or the parking brake calipers. I'm sure I'll get flack for that, yes they all work, but nothing holds as good as properly adjusted drum brake. And no the self-adjusters never work, I've never seen one work, I've never heard of one actually working, so who knows. I've always had to go back in there and adjust everything manually every 3 to 6,000 mi depending on how and where said vehicle is driven. I don't think we need to get into the discussion though of what it's better disc or drum. Because in the end if you end up locking up the wheels it doesn't matter at that point. The whole point is better more linear control of the brakes before the wheels lock, and how do you achieve that without re-engineering the wheel
( see what I did there ;)