One swings from the top, and one swings from the bottom. And Ed has done tons of research on this subject, and I suspect you'll have way more info than you need...
Curious if they are the same size and if they use the same bezel/mounting hardware. I really liked FredR's gain controls on his 400's and wondered if one of Joes new 700b faceplates could be added to a 400 if one was going to add gain controls and a power switch.
there was a 400 on Flebay that a guy added a 700b faceplate, meters and gain controls to a 400