I'll share with you what little I know about the old 6.2 Diesel. My dad works for a mining company, and the only vehicles that can be driven underground are ones that are diesel powered. This is because diesel fuel has such a high flash point, where as gasoline has a low flash point. Simply put, by running gas powered vehicles underground, they run a high risk of explosion.
Anyways, back the the subject on the 6.2. At the mine, they had 5 Chevy 4/4 3/4 ton pickups, 2 1986 K-20's, 1 1990 K-2500, and 2 1992 K-2500's. All were equiped with the 6.2. These trucks put up with so much abuse being driven underground on the rough roads and hauling equipment. You have no idea until you have ridden underground in one of them. In some cases, Dad said they even drove them in water up to the tailgates! Out of the 5 trucks I mentioned above, Dad said the '86's were the toughest of them all. They had the solid front axles, and were essentially built using old school technology. This is the same body style that you are thinking about buying. The independent front suspension on the newer trucks could only take abuse for so long. Broken torsion bars and busted CV joints were common, and the water that got into the differentials would eventually ruin them. All of the 6.2's in the trucks faired pretty well. With the exception of one, it was one of the 92's. Somehow, something happened to the front driveshaft, and it came off and sliced open the oil filter, which was mounted just above. The man that was driving it wasn't paying attention the the gages, and all the oil ran out of it and locked it up. They ended up putting a Goodwrench rebuilt 6.2 in it.
Dad's company truck was one of the 86's, and it was a damn good truck. It had the bulldog low 4 speed in it, and it would just about climb a tree. With the exception of a leaky injector, it ran great all the time. In cold weather, he would make sure and put conditioner in the fuel, and if a power outlet was nearby, he would plug it in at night.
He let me drive it a few times, and I can say that this truck was strong but the old 6.2 just doesn't have very much power. Plan on holding your foot to the floor quite a bit. There are aftermarket turbo chargers available that make these engines actually quite powerful from what I have heard. I will tell you this, I would have an old 6.2 versus a new 6.5 Turbo diesel that GM offers now. The 6.5 may be more powerful, but it's had a lot of problems over the years. They have one of these at the mine now in a one ton flat bed, and it's been nothing but trouble. It's a 96 and it's on it's second engine, and it's not even an underground truck. Well, I'm gonna rest my case now. I hope that I've helped you some here. Hope you enjoyed the mining story, there's a ton more to tell, but I'm tired of typing ...LOL