I'm new here so hope I'm putting this in the correct place. I have a 94 Chevy 1500 and I blew a head gasket so I decided to rebuild the engine. This will be my first rebuild however I am familiar with just about everything to do with it. I pulled the driver's side head off and this is what I found. The valve on the far right has a square notch cut out in it. Can someone xplain this because I've never seen or heard about this anywhere. The engine looks to be in excellent shape it's just this valve has got me scratching my head. So do I need new valves and what all is involved in rebuilding the head. Thanks in advance. I've included pics also.

 

I've never seen a valve like that. I have no way to know why its there, but Id get a new valve and forget about it.