How NOT to build an economical or powerful 'teen

273, My heads are stock closed chamber 1965 273 castings. Stock back cut valves & mild port work. Domed hi-po 273 pistons from kanter. It has an isky e-4 with crane iron 1.6 rockers on it & a ld4b made to fit my early heads. From 2500 to 5700 it pulls like a little freight train.Idle vac is 15-16 @ 750. Dont know power output but im sure its not far from the teen. Im sure headders would help even more but I like how stock exhaust sounds, works & fits.