It really hurts to see that cap. It's unfortunate but... buying a used engine is always a gamble. This teardown will give you a chance to confirm the rest of the engine is in great condition and you will have peace of mind that is reassembled to your standards.
Nice job cleaning the timing plate. I would probably think about replacing the well used countersunk screws in the timing plate with Allen head screws if they are available.
Following up on the comment about Roloc discs, it's probably a bad idea to clean any internal engine parts with abrasive discs. The abrasive material erodes and ends up all over inside the engine. Better to use a bristle disc.
