GT40 Heads - What kind of difference will I see? 1988 Mustang

I just bought an 88 with a mostly stock 302 with some pretty good bolt on stuff.

Cobra Upper/Lower
Cobra ECM
Cobra Fuel Rails
24 lb Injectors
65 mm Throttle Body
73 mm Mass Air
155 lph Fuel Pump
MSD Ignition System
March Underdrive Pulleys
3.73 Gear
Super HD World Class rated at 330 lb with a Zoom Clutch

Anyway, what kind of difference will I see adding a set of GT40 (non p) heads with 1.72 roller rockers. I may even go with a cam if I can get an idea of which one would perform the best with my setup.

Thanks!
Bill