Seeking some advice - 1990 K3500 6.2HD Utility truck

New guy, first post. If this thread is in the wrong subforum then I apologize. Also if I happen to leave out anything important here then please let me know and I will add it.

Starting at the beginning - I recently purchased a 1990 K3500 with 40k original miles. As I understand it, this truck was originally a special order for the fire dept. in a small town around here, but they ended up not using it, so it was then sold/sent to the water dept. in that same town where it was then used for 25 years (thus the super low miles). The first thing I did after purchasing was take it by a local shop where I get some work done, and have one of their guys look it over. This individual co-owned a chevy dealership for about 30 years so I figured he would be able to tell me more about what I had. His answer surprised me a little, and that's why I'm here. He claims to have never seen this exact configuration before, which could have something to do with it being a fire dept special.

Here's what we have:

• 4x4 but its a split diff with a skid plate (according to him, it should normally have had a solid axle)
• 16" 8-lug wheels (he believes that stocks would have been 19")
• 159.5 wheelbase - (this is where he explained to me the difference between a cab+chassis configuration, versus a simple "bed delete" option on a normal truck, with the different frame-rail spacing, axle width, etc. He was a little bit perplexed because he couldn't tell which one it actually was. Also said he thought this length was common for a crew cab, but not a single cab)
• He ended with saying that because this was the body-style change year for the 3500, this was the first year of these and it could be some one-off deal due to that.

I realize that this guy could just be old and confused. He could also simply be full of crap. Thats why I'm here.

So what do I want? Two main questions, at least for now.

• I bought this not realizing it might be "special", just hoping to adapt it to pull a camper. I'm curious if there is even anything I can easily fit on the back, to replace the utility bed that is there currently, since thats not really convenient for my intended purpose. I have no idea where to look for such information, and even if I did, I'm willing to bet that without knowing exactly what I have, it would lead to some pretty confusing results. I thought about trying to fit a 8' regular bed on it, but then that leaves a ~3-foot gap between the bed and cab. I've seen this configuration a time or two, with some sort of frame-mount basket or something fitted in between to take up the space so it doesn't look stupid. Any advice or suggestions, first-hand experiences are much appreciated.

• Whats the deal with this engine? I've read some pretty mixed things about the 6.2HD, but most say that its made more for economy than for pulling, even though this is a 1-ton truck. If this is the case, then I may be better off trading it off for a cummins or something. Again, any advice is appreciated.