Need Advice On A 68 Shelby

I am about to purchase a 68 Shelby and don't know much about the Shelby cars. Can anyone educate me on what to look for in a Shelby car in this case a 68 GT 350 and a 68 GT 500 KR? I think the cars are beautiful but I am an amateur and don't want to pay for something and end up getting something else. Something I would like to know is how to decode the tags under the hood. Anything else you may thing I should look please let me know.