GMC rear bumper bracket help!!!

[JQ-72]

I'm in the process of converting my 72 Sierra Grande from a lwb to swb. I used a doner frame instead of cutting. The doner frame is a 69 or 70 GMC shorty. I'm installing a factory style chrome rear bumper but the holes do not line up?!? I've got a 69 Chevy frame here for comparison and the distance between the mounting holes is different and the actual location of the holes is different (I measured from the rear of the frame up to the first mounting holes and they are different). Did GMC's - or Chevy with leafs - use a different bumper bracket on short wheel bases? Thanks for any help.
Joshua

[dakman]

the short and long wheel base frames with leaf spring suspension use different inner rear bumper brackets due to the shackle bracket location on the frame, it gets in the way on a swb where as the lwb frame extends far enough that it's not an issue. You'll need the proper brackets for a swb leaf spring truck. I found out after a lot of research that pretty much all the brackets are interchangeable between the years and GMC/chevy except for a swb leaf spring truck, it pretty much has it's own.

Here's what they'll look like, notice the inner brakets look similar but just a bit different. I forget the part number but several places carry them for around $60

[71 super]

The innner brackets are the same brackets used for swb 4x4 and swb leaf spring gmc. They are roughly 65-75 dollars. Wes has a set as do some others, but regular inners will not work, they must have the inner structural support added as pictured previously.