e57, you will not find that setup for 4 sq or 4 11/16. Hubbell makes a plate S320. It is a three gang plate. The center is blank with an L5-20R hole in the 1st gang and 3rd gang. It is smooth stainless steel. This is the only way I know you can put 2 L5-20R in the same box. Hope this helps.
Al
