The only pic that I have of those rear sets on my bike is here.
http://www.geocities.com/fischervintagecycle/projects.htmlThey aint the prettiest, but work fine.
The 3 holes are for the foot peg mounting.
I had those on my bike years ago, so the details may be a little fuzzy (or wrong

)
One of those clamps goes on the front, around the down tube. One clamp goes near the rear muffler hanger (bottom of plate- I beleive it is the odd hole behind the 3 peg mounting holes)
The peg bolt also went through one of the frame clamps(above the rear muffler hanger) I beleive I had to drill the clamp out to fit the peg bolt through it.
I beleive the front mount (clamp) also had a spacer to move the front of the plate out some(you could probably use washers).
Like I said, the details are a little fuzzy, but when you start to put them on, it will come to you.
Start with the rear bottom muffler clamp and it should "fall" into place.