Oh man, your face! Kid in a candy store. I need a chain cover for a 503.
I also need a couple 310 trimmer parts. Seems like you might be the man to talk to.
My wife took that photo. She was amazed at the mess since I usually keep the tools stored in various places.
For repair parts for vintage Porter Cable tools, the below link is probably the best source that I know of.
North Canton Repair Shop