what 4 speed auto transmissions can i use? 46rh etc

Hey guys
I had a transmission shop tell me today that the a500/42rh transmission will not work behind my 5.9 magnum. He said the a500s were only behind the 5.2 but I am sure I have seen posts on here of them behind 5.9s.
I don't want to cut the whole floor so don't really want to use a a518.