No need to go 2.4 or 2.3 to get more power (unless you are looking for that low end torque like myself), plenty of 4g63 cars running 500+ on the 2.0. E85 if available in your area will help achieve your goal, but even on regular pump gas it's attainable.

Terry is right, get some bigger injectors as you are probably running out of room on those 660s and tune it some more. Also which Walboro pump do you have the 190lph or 255lph? Asking since you didn't specify. The FP Green is more than capable of reaching 400hp+.

Tim Reed
76 Colt Galant coupe
77 Colt Galant Wagon
91 GVR4 1350/2000 (Scrapped)
99 Eclipse GS (sold)
89 Suburban 4x4