17" rims are what the 3800's came with.
Your truck probably has a 14" rear drum
On most steel 16" rims, the rib that the wheel center welds to, narrows down to 13.5" Depending on where it narrows down at, a 16" rim may work.
The problem with the early rims is that the center band is pretty wide.
Try your 16's on the back to see if they work. Otherwise you need a different rim.
