[fuzzypuppy]

I see from your profile that your truck is an 89, if the engine is original then more than likely yes your engine is a flat tappet with provisions for a roller valvetrain.
The major difference between the two is in the lifter, the bottom of the flat tappet lifter has a flat surface that rides on the lobe of the cam, thus the term "flat tappet".
The roller style lifters have a small steel wheel or "roller" at the bottom which rides on the lobes of the cam.
None of the parts between the two are interchangable, these being , cam, lifters, pushrods, as well roller cams need to have what I refer to as a "keeper" at the front that bolts to the block to keep the cam from "walking" or moving forward out of alignment.
Flat tappet cams do not need this.
The reason you can choose between the two set ups is because your year block more than likely has tapped holes in the front of your block where the cam slides in to bolt on the keeper ring for the roller cam.
"I don't know how better to explain this last part so I hope this makes sence"
I suppose the best argument for going "roller" would longevity, a wheel rolling on the lobes of the cam would cause much less wear, heat and friction than the flat surface rubbing on the cam lobes of the flat tappet style.
The timing chain for either is the same, though if doing a cam swap I would advise changing the chain and gears if stock, if only because everything is already opened up and ready to do so, chain and gears are cheap.
The "roller" in roller timing chain has nothing to do with your valve train in the way you may be thinking.
The "roller" in this instance refers to the chain itself, the pins that hold the chain links together are what ride on the gears, in the roller style these pins are surrounded by a tube that roles on the pins, "here again less friction", as well you avoid having the same point on the pin rubbing the same point on the gears over and over as the assembly rotates reducing metal on metal wear, heat and friction.
Longevity would be the key word here again.
Your choice in setup depend on you, the old flat tappet style are just fine for everyday use.
If building for performance and looking for every pony you can get, go roller.
The one thing I can't stress enough is that whatever setup you choose, follow the " breakin procedure" exactly.
If going flat tappet be sure your engine is ready to run the full 20 min before shutdown, plenty of fuel, water,and get the timing as close as you can, just follow the instructions that come with your cam kit.
I have seen friends lose a cam after only 2 or 3 k just because they did not breakin properly, and this usualy because they were just in to big a hurry to "get the thing fired".
Long post I know but just a line or two really would not explain the questions you asked.
I hope this helps, good luck with your install.