My dad ran a pure stock mustang for awhile, and a good way to start would be to short belt the engine where only the water pump and alternator are being driven by the crank. Next would be to use an aftermarket shorty header with an H or X pipe and good mufflers. Then change the gear to somewhere around a 3.73 or 4.10 with a good Drag Radial tire, I prefer Mickey Thompsons. We changed to an aftermarket axle but some people keep the stock axles. Also, you will probably need to rebuild the posi-trac and a regular kit from Ford racing will do the job. I believe we ran a best of 8.50 on a 9.30 index in H/PS without much else done to the car. Most of the time we were in the 8.70s but the converter is the key. I drove this car to high school and we got 20 mpg on the interstate
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-Jake