Having built a road race car from scratch, I can tell you that anything can be made to handle well, but where do you cross the comfort level? My Suzuki ran great and it only had a 98" wheelbase.

Getting a car right requires more than just a shopping list. Testing at the track is where it gets sorted out. This is where you find that the springs are too stiff (or not stiff enough), the shocks get adjusted (or replaced), the swap bar is adjusted (if adjustable) or replaced with a different size.

Don't take this the wrong way, but this is where the driver also gets sorted out. I know I'm not the fastest driver, so I know I have plenty left in the car. Some tracks I know far better than others. I know I wouldn't pick Road America to sort out my Suzuki. Whatever car you drive, take a driver's school and learn to get the most out of you and the car you're driving. My instuctors always advised to maximize the driver first before making changes. After that, you'll know where to make your changes.

Mustangs are excellent cars, but always finished second to Camaros in SCCA Showroom Stock. Check out the rules for American Sedan at SCCA.org. Maybe check out an event at a local autocross or regional race. Autocrossing is an extremely safe way to test the car without being a danger to you or the car. And have fun.