This is exactly what we did to put a magnum into a 65 Valiant. You'll see some writeups that show modifying the other mount. I found a writeup explaing that was a mistake made made by some engineer who thought the "right" side mount was as viewed from the grill, i.e. the drivers side. Not sure of thats true, but the correct one to mod is the more "square" one like this diagram shows.
