New from Iowa

Hey all, I'm new to this forum and interested in the '66 Cuda. I'd like to get a 'S' model-of course they're pretty rare and may settle for any 273 model. A couple questions for you though. How can I tell a true 'S' from a regular 273? The VIN won't tell me that, and if the data plate is missing how can I be sure? I know the 'S' had a tach but I haven't seen a pic of it to differentiate it from the vacuum gauge. And of course, the 'S' badges, but did the speedo go to 150mph? How about the motor, is there something obvious that tells me it's a commando rather than standard other than 4 barrel carb?
Many questions...

Brian