Whose got a leaf rear end that can help with sport bumper brackets?

[hpcgmc]

I'm still trying to get the sport bumper brackets to work on my 1/2 ton short bed leaf spring truck. I ordered the brackets for a leaf spring rear end, but I cant find any holes in the frame that line up. What I need to figure out is where the holes should be in the frame, so when I drill the holes, the bumper will line up correctly.

Here are a some pics - pic one is driver side behind the frame rail, pic two is driver side forward of the frame rail. Pics 3 and 4 are pass side forward of the frame rail. As you can see, the end of the brackets bump into the rivet heads, so I might have to trim the brackets as well as drill them.

If anyone has pics or explanations of how the brackets should be attached forward of the frame, that would be great!