in all honesty, don't change it. You have heads that won't allow your engine to rev past about 4000, and a relatively small bore that limits breathing. The intake and carb weren't what was holding you back. The new parts might have given you 15 hp, but you have to change those heads.
Engine power is based on a matching of all parameters: carb tuning, intake flow, head flow, compression, cam events, and exhaust. Simply changing to a performance cam, carb, and intake will mean you have a carb, intake, and cam tuned for higher performance, but heads, compression, and exhaust tuned for stock perfrormance. The net result will be a mismatch. Not only will you not gain any performance in the higher RPM range, you'll lose performance in the low-rpm range. Your performance will suffer big time.
I won't get into the finer points here, but all performance parts need to be matched together. You're starting with a small-bore engine, so you have to be extra careful with your choices.