If your mustang is mostly stock the A-trim kit comes with everything you need. Your injecters will be fine with the fmu you get with the kit. You can even get the S-trim and use your injecters. It comes with the fmu, fuel pump, and boost retard. Unless your looking to do heads, intake, exhaust, and a cam change the only thing you need is a bigger maf so the blower can get the air it needs. But if you are you will need bigger injecters with a calibrated maf for the added air flow.
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NA 347 W/ stage 2 Canfield heads, out of the box Victor 5.0 intake, solid roller cam, Aeromotive fuel system.
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