That IS a genuine 5513/1680/1665 insert. Just google "5513 midfont". May not be period correct for a PCG, but it could have easily been a service replacement.
It would not fit on a sapphire watch.
Agreed with all except that you can reach the spring on an ETA 2836-2 and similar, since it sits up so high. See my tutorial: http://www.rwgforum.net/topic/159437-removing-an-overlayed-date-wheel-without-a-screwdriver/
Just like Tomhorn says, it's an easy swap. Just slide a razor blade under the existing bezel to loosen it, pop it off with a case knife, an press down the new bezel. I might take you give minutes.
Maybe check with the seller on which models this fits;
http://bit.ly/1mTSq4s
Good luck.
Between those two, I would go for the MF. Maybe ask about the brown spotting (rust?) on the case neck. Look between the rehaut and the insert between 10 and 20. Does it affect other parts of the midcase or bezel assembly?