I have that one or an identical one.Assuming you live in the rust belt, you need to use a file or a sandblaster to clean corrosion out from the caliper brackets, under where the abutment clips mount. A wire wheel won't cut it. They just polish the rust. I got this wrong for decades and struggled with some brake jobs.
Here is the file I use. It was an SMA channel recommendation that I took years ago. It's German made and is specifically designed for caliper brackets.
if you use a brake caliper bracket file it wont remove metal from the bracket. Its really good at getting crust out of the corners of the square slot.Here in the rust belt, you often have to LIGHTLY LIGHTLY file the caliper bracket slots where the pads (or hardware) sits. You don't remove metal though, just grit, rust, etc. Some people might think they need to file the mating part though.
OP is using Raybestos Element 3 parts and I haven't seen anyone mention having to make them fit. I'm afraid the OP has something else going on....