It looks like the PO replaced it in 2004 judging from the archeology evidence you have there, so it was time to replace again.
All kidding aside, it looks like you may be in for a little more engine work than you thought at the start of your project. I am not the one to pass judgment as I have not yet tore an engine apart here, but there are many thread on this beauty. Good luck and make sure you keep our eyes' needs fulfilled with lots of pictures on your quest.