The front treatment on the yellow coupe is very art-deco looking to my eyes. More an artifact of the 30's than the 50's, but I like it. I think any additional trim between the body and the snugged up bumper would look best if kept very simple and thin, just enough to define where one ends and the other begins.
I agree, the trim would have to be understated. Here is another example, however I think it could be thinner as well as shorter. It would look better to have the trim from the yellow Gmund done without the license plate surround, just straight pieces.