Heh, I work for safelite autoglass. If your mustang is not a fox, you need to take off your a-pillar covers, then cold cut the top and 2 sides, then use a long knife (razor knife with long handle) to do the bottom. If it is a fox, the cowl and all the metal trim needs to come off, then you can cold cut the whole thing.
OR you could just pay like 75 bucks to have a glass guy do it, usually much safer.
-Joe