Unfortunately not all engines respond the same but you did find 400 free RPM. You may need to open up or at least polish the carb throat to gain enough flow to compliment your port mods , that and the exhaust may be restricting it also.
I will take any free 400 rpm I can get any day.
So tell me, does it run "better"? More responsive? Crispy, like we used to say at the dragstrip?