Question regarding vin and model numbers

[REDROCKER652002]

OK, so my son and I bought a beat up old 69 C10. He has since decided he does not want to work with it anymore so I am taking it over. Before he quit we redid the wiring, exhaust and some interior stuff. He ripped the bed wood out and that is where is stands. I want to replace the cross sills and just put a piece of plywood for the bed right now. As I have looked more into it, seems the old owner moved one of the cross sills down and redrilled a hole for one of the others. Now, my question. In looking at the VIN and Model, I am wondering if it was a fleetside to start with and someone decided to change it to a stepside. Here are the numbers I found.

Drivers side Pillar: CE149Z897007

Inside the glove box: C#141z606130 and CE10934

I have looked around and I cannot seem to match the numbers exactly, but I have a sneaking suspicion this was a fleetside that somebody turned into a step side. If that is the case, is it possible to keep it as a stepside? I like the look of them better anyway.

Any input is welcomed and appreciated.