I dunno why I didn't check out Bench when the original poster suggested him, but it looks from what I can tell that his 1974 (708 PA) is the most PA by anyone who played primarily catcher. He played 160 games, but only 137 at catcher (also playing 3B & 1B), so there is that.
[b:8a5b36a1f5]BK[/b:8a5b36a1f5], nice catch (no pun intended) on the guy who caught every game! I had no idea about that; I'm shocked and impressed that someone could do that.