Your stock ignition coil is fine. Did you get a graph from the dyno facility and is that something you could scan and post on here? Did it just sort of flatten out at peak HP?
Let's run some numbers here real quick and calculate to what degree your pump is limiting you. 88l/h * 1.5625 lb/l = 137.5 lb/h. Divide that by 8 and you get 17.1875 lb/h distributed across the injectors. Multiply that by 16 for total possible HP (assuming .5 BSFC). That's a max of 275 HP. Don't expect to get 100% out of your fuel pump, either.
Factor in 20% loss for AOD and you get about 268 HP at the flywheel. It's scary how much the numbers match up.
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351W 89 Mustang GT Convertible