Most magazine ads are small. It's hard for people to see them.
To display one or two at a show with your car, you will want to scan them and print them as a larger poster size print, probably mounted to foam board. You don't even need the original ad for that, if you can get someone to send you a good, high-resolution scan to print from.
If you can get a larger size ad, like from the Saturday Evening Post, scanned for you, you'd be in business!
The original ad I have for my '29 Phaeton is quite small. It would not blow up too well.