I love imaginative thinking! Maybe I'm just bored with the cars I have seen over the last 50 years. Many of the things that are done are either because...

...builders have been conditioned to only think within certain limits...

...they are trying to build in what is considered a classic or nostalgic look...

...or they are afraid that someone else might not approve, or even offer criticism.

You could create your own design, as you have suggested, maybe inspired by the popular Olds air cleaner of the fifties or a famous rare piece of speed equipment... or look at other things going on during the era your car represents, like that newspaper box that was used as a scoop on many race cars... or even be humorous, and use something like a sombrero, a mailbox, a tool box, or a hubcap. Maybe you could even think of something with a personal meaning to you.