RARE!!!! Info Appreciated

[Choat_Stepper]

Here is my 1970 GMC stepper that I had previously spoke about. We bought this truck 13 years ago. It is a barn find from an older gentleman down the road from me. The story we got was that there were only 7 of these trucks made. They were built for a phone company I believe. A tree had landed on the passenger side and got the cab and door pretty bad. It was still drivable so it became ours. It is equipped with:
Bucket Seats
Factory Tach
4 Speed w/ Granny low
396 BB
no power steering or brakes. Here is the SPID from the glove box. It shows as a half ton. Not sure of why or how it became this way. Any info would be greatly appreciated. Just wanted to share with you all knowing it would be appreciated. Also here are a couple pics of my dad's 4x4. Thanks and have a great day.