I got this old truck!!

I need some help in figuring out if I have a rare 1 of 500 vehicle or somebody did the best and I mean the best job on this kit that I have ever seen.  I bought a '79 Chvy Suburban Dually back a couple of months ago and was trying to get to the bottom of this things life.  I started at the BMV just to find out how many time that the ole girl has been handled.  Come to find out that I'm the third owner of the truck.  Next because of the VIN that is on it that starts with two letters instead of a 1. Now I have had a couple of older trucks in my time and so have a few of my buddies.  And I remember that not a one of their vehicles car or truck started with 2 letters instead of a 1.  Teh first three things that show up on the vin are CC1 and so on.  The next thing that I did was to try to get ahold of the first owner of the truck.  That led me to a man that had passed, but the brother was still around.  He told me that the truck was bought from the dealer like it was.  So I just assumed that they really did make a truck like that.  Next thing that I did was to inspect it for age marks and difference in wear of the parts that would have been put on as a kit.  I was just looking to see if the kit was recent or if it was old.  Well I'll just say that the fenders are sheet metal and the 1 ton suspension that is on it is showing some descent wear.  Now the truck was labeled as a C10 Suburban.  Now in the glove box is a blue and white sticker that has GM replacement part numbers oon it.  Now as you go down the very long list of options that are on it you come to a part that says Silverado package.
Kind of odd I thought and the dash does say Silverado on it.  Can anyone in here tell me if they did or didn't make these trucks factory or did the dealrs put this stuff on, or was it ordered that way??  I have a few guys that say they are GM gooroo's and that they never made the dually factory or otherwise it was always a kit truck and the kit has to be a certain kind.  Thanks for reading my rambling I tried to keep it short.....  

These were never made at a factory, but some dealers installed aftermarket parts to produce these, if you search around the web there is still kits to do this conversion. One dealer in Oregon went as far as to swap 1 ton running gear and fenders on a Blazer to make it a dually.