Speaker sizes

Well you can put anything you want as long as your willing to pay for it or build it. Check out this website http://jr.stangnet.com/mustang.htm

This guy did a great job. I plan to do alot of the same stuff to mine. As for the sizes. The rear package tray can fit 2-3 6x9's. Get in your trunk and look underneath the package tray, youll see 3 6x9 holes. As for the doors? You can fit some small speakers in them but I would build you own kick panels like on the website or buy them. Alot of companys sell them. The only other speaker is in the dash. Its like a 7x3 or something. Different companys make different versions. Theres one thats got 2 small speakers instead of one large one. Im planning on using Infinity Kappa's all the way around on mine. Alot of people like Focal's also(way to expensive for me). Im gonna get some 6 inch componet sets for my custom kick panels, different dash speaker(the 2 smaller speaker version), 2 6x9's in the package tray and a single 12 in the trunk. For my sub I plan to use a speaker made by a guy localy named Toby(Team Toby). There subs are awesome Iv got a single 10 with a 100 watt 90$ Kenwood amp in my firebird and it sounds better than most of my friends systems. Well hope this helps you out. Check out that website, that guy did alot of kick ass stuff on his car.