Wait a minute. I never heard of a 5901 hooker (I don't use 1.625 tubes on anything) but that number shows they fit an Aspen. That's not an A body. They may for an A body but the summit sight doesn't show they fit A bodies.
If they don't fit an A body, that the problem. If they will fit an A body, the shop was incompetent at best. Find a speed shop, not a muffle shop to put them on. Better yet, try it yourself.