get a grease pencil and some blue painters tape the same width as the space between the stripes, 1 1/2, 2 inches, whatever.
using a tape measure and the pencil, find the center of the car. I measured from the edges of the hood, glass, and trunk. by the time you do the bumpers you can do it freehand. you can use strips of blue tape to write on and make measurement marks to.
lay a stripe of blue tape down the center of the car. measure, move the tape, look from every angle, move the tape, hood up/down, have someone else look at it, no joke. It must look centered and straight. whatever the tape measure says, it isn't right untill it looks right.
Use the centered tape as the guide to float your stripes up to and don't worry about the outside of the stripes.
I did not use a "kit". I had bulk vynil cut to width and then had to stretch it as I laid it down. kinda sucks.
I floated it on (using a hand bottle sprayer with just a few drops of dish soap in water) by spraying the car wet, lay the stripe down and squeegee it dry with a high density sponge a soft squeegee. be careful not to scratch the vynil. be careful not to wrinkle or tear it. air bubbles are not that big a deal to work out, just be paitent and don't hurt the vynil.
BYW, you will never blend in again, unless you are at a Shelby meet.
__________________ 05 GT Premium stick. Satin Silver w/ dark charcoal IUP, dark tint and stripes. Shelby wheels and pedal covers-Cervinis 500 front splitter-Hurst equipped-Meziere pump-JLT II CAI-tune by Brenspeed... Love it!!
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92' LX Vert for the son. 2.3 auto Black on White with Red
89' BMW 325iC, black on red on black, stick Beater car
84' Porsche 944 black, stick. motor is apart, stupid car | 
Need help installing Shelby stripes 
