Thanks for posting the Bob Wingate story links and picture, he was certainly a big factor in developing that dealer's reputation and high performance status. Also good to hear you enjoyed our own 'left coast' during shore leave!
Austin you can see in the picture I posted of both plate frames, that the rear one has 2 extra mounting holes drilled along the bottom. Suspect that was pretty common; the single plate frame posted just above this on 'WPH698' (also a rear plate) has a hole drilled in the bottom centre, although it looks like the earlier frame style that has 2 spring clips to hold the plate in place.
On the original dealer lot, from research about a year ago the property had been sold for development and I believe the sign was gone. The owner had fallen foul of the City of Covina IIRC as I found some online articles on that.