Matt is correct about if you are planning on showing it at a national meet, then yes you really need to restore it back to the way it came from the factory.
If you are only planning on going to local type meets with it then it depends on which meet you go to. There are some AACA local region/chapter meets that are strict as national on modifications, then others will let some things slide.
Then other show who knows. If it is people's choice to determine than anything goes. There was a show near here that was hosted by an orgiazation and a nearby street rod club judged it. There was classes for stock Chevy II/Novas and one for modified Chevy II/Novas. My dad and I had the only two stock Chevy IIs in the meet. A guy with a Chevy II with ladder bars, full rollcage, street drag tires took home 1st place!!!

Obviously modifications didn't matter there.