Before I get to the suggestions - consider that the main reason for going to a car show is to let other folks see your car, see other cars, and have a great time wandering around and talking with people. Enjoy the day and have a fun time.
For the poster, it can be pretty much whatever you choose. Not for our cars (I hope!) but a number of ones I have seen will spell who did the engine, who did the paint, who did the custom work, what type of engine is in the car, and that sort of thing.
For the Pagoda, you could do a short history of the 230 SL, sort of like a lot of ads do - the generic about six cylinder, mechanical injection, designed by, etc. Is the show an "all marques" kind of thing? If there are not many foreign cars, the above information would also be educational.
If it is an original car, that sort of thing. Or if there is anything unusual or interesting about the car, kind of a "prime the questions" conversations starter.
I would not obsess about the poster, and I know there will be some better suggestions, and hopefully a photo or two. I did try the search function, and did not have much luck, so if you want to poke around with that you might find something
