What year Cobra? If you are thinking about the Windsor based 351, there a big difference in the wiring harnesses due to different ignitions (coil pack vs. ditributor) and other sensors. Plus the 4.6's use the EEC-5 computer where as the Windsor models (302 & 351) used the EEC-4.
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Good luck!
Brad R.
1992 L.X. 5.0 coupe
MODS: A few little bolt ons 
New Best time ...11.60 @ 128 mph @ 2000+ ft altitude.
Rice Haters Club member #39
Users rides #2542
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