I have never seen a c10 quite like mine.im wondering if it was a rare find or just a custom order from factory.

That IS rare. Be careful, and don't let anybody beat you out of it.

If your truck was solid Orange on the bottom with a chrome divider below the rear window all the way around the cab to the doors, with the White top and then the upper fender chrome only , it was a specific option order... there were quite a few like that though. They were a cheaper option than having both upper and lower chrome with a different color in between. Although... having the 3 tanks... was a rare and special order option only... If it has an Automatic, and power brakes even with or without disc up front, or with Power Steering, Those were all optional also...There were also several rear end choices as well as wheel/hubcap or Ralley Wheel options too.