Today I received my copy of Model Railroader's "How to model Railroads of the 1950's". It contains two great photos of 1950s diners that match pretty well with Plasticville's diner. Well, except for the entrance, there is a 'mudroom' at the front door (an addition to keep the weather out. This looked so much like I remember diners that I decided to add one to mine. Fortunately, I had a couple of parts (two complete end walls and a portion of the front wall that contained the door) from a second diner that I could cut to fit my diners front door.
So far I have cut a side door and the front door to less 1.5 inch wide, so they will end up being opposing entrances. I then cut from the end wall that only has windows, one window with complete side designs. This piece covers the space between the two doors. This addition will have a flat roof and the window will have a sign that reads 'open'.
You can see from this photo of the Relish Diner in Brooklyn the entrance I am trying to describe.
The only problem I see will be matching the chrome of the original since the new parts are grey. Hopefully some photos tomorrow.