I bought the same vented cap with ears as Ragu, but was able to easily modify it to fit. It won't win any awards but it doesn't look that bad and it works! I just couldn't find a reproduction and originals are impossible to find. I was also worried an original would get stolen, so I didn't want to have to take it off and take it into the store with me!

I was reading some older threads on this site where someone drilled holes in their caps so it would breath both ways. I think somone said their sending unit blew out of the tank because it got hot in the garage and the pressure built up. So when I had the fuel filler neck out of the car I put my modified cap on the filler neck and blew hard on the other side. It let pressure out from the cap when I blew hard enough, so I didn't see any reason to drill holes in my setup.
I'll snap a photo of it later.