It's hard to tell by the picture, but GMC used a 5 lug pattern on some trucks. The studs are larger than the typical Chevrolet pattern and the bolt circle is bigger as well.
If you found a set of rear drums and hubs from a Chevy, you could probably swap them out to make all four wheels match. It's pretty simple.
What does the bolt circle measure? And what size are the lugs?
Jeff
