I had one of the original Andersen on my first 21 Escape, it had the universal brackets which were too large. I stopped in Idaho Falls, Id at their factory on the way to Osoyoos and had the fortunate opportunity to meet Jason, their representative who came out to the parking lot and put on the right sized brackets. I believe item #3343 for 4" frames is what you want.
Due to the pandemic, my life now exists of only 3 days, yesterday, today, and tomorrow. Everything else has been forgotten!