I have the same thing on my trucks. I was not sure if it was a year thing or a GMC/Chevy thing. Seems like a year thing from what I have heard, 47-48 used 2 springs and single after that. They all have the same part numbers and I have not found a written reference anywhere. My hinges on my stock 47's have two springs. The hinges on my 48 also have 2 springs. That truck was well worn when I got it so I can't attest to originality. The 2 spring hinge is different than the 1 hinge spring in the shape and length of the stop that is on the hinge. The 2 spring hinge has a smaller stop and allows the door to open further. You should use a matched pair upper and lower so the door is stable at full open. They are tricky to get in and out of the pocket. They should also use the 4th bolt on the inside plate. It will make a difference when you are aligning the door again.
