I used the Surco's and had two more made based on their design. Because my rack is longer than my roof, I wanted to use all 6 mounting locations.
If you go to the "Hall of Fame" Tad has a write up on how to get to the factory holes.
Also, be sure to get the proper bolts. I cannot remember them now, but I think they are 6x20-25mm. I can check tomorrow. I got mine at Lowe's.
I will take pictures of how I mounted. I took a bolt thru the rack-unistrut-bracket.
After chopping up my rack, I ended up with it exactly in the least best place, if I was 1 inch wider or narrower, I could have mounted to the cross braces, but as of now, they just serve as some further support and a spaver to keep the racks braces off the roof of the car.
Pic's tomorrow.