FastCraig, take a close look at the illustration on your instructions, looks like you might have the same problem I had. The radius around the bolt holes need to match the picture exactly or you have the C10 mounts. I had this issue and thought I was crazy but they claimed that they have had misboxing issues in the past and that’s what happened. They sent me out the correct ones.
If you look at the attached picture you can see these are the wrong mounts.
Now, they still won’t clear the stock truck compressor unfortunately, even if you notch the frame, it just won’t clear the compressor bracket.
Also, Anubis, you’re incorrect when you say that the mounts work if you put them in the Holley location. I think a lot depends on the build variables, but in the Holley recommended location it won’t clear the heat/ac box. I moved mine to the forward most holes to get it to clear, then swapped the