The original rack bolted down from the top into some weld nuts on the blazer.
I used these with a fender washer pushed up from the bottom/inside to try and spread out the weight from pulling force.
I found these a local hardware store, they are a Hilman branded threaded insert, but I don't know the part number.
I installed them just like it is in the photo, and then used a button head cap screw down from the top.
I was able to keep the insert from spinning by holding in those holes with a snap ring pliers, like a spanner wrench.
I didn't want bolts sticking down inside, but they would probably be just fine, or you could use acorn nuts for a more finished look with no sharp edges.
But with these it's flush except the flange of the insert and the fender washer.
I seem to recall someone doing something similar with a Ford Explorer rack too.
The other option is some Yakima rails and racks, but it got to be more expensive than I wanted to invest. But it was a really nice setup, and the cross bars can be taken off when you're not using it. So, it has a cleaner look.