Need Help for my 318

I have a Dodge Dart Sport 1975, and i have this parts working now:
318 engine 1975 low compres (put 1970 heads).
268-272 mopar camshaft and lifters hydraulic
Edelbrock Performance manifold
600 cfm edelbrock carb
Edelbrock springs
Edelbrock chain
Hedman Hedders
904 torquerflite
3.55 posi rear end 8 1/4
Original electronic Ignition

i have 2 questions:

+ Why my car only goes to 4000rpm? A friend said that i need a new electronic control box...its that true...or it could be another thing?
+ What can i do to get more Hp, with that parts....or what recomend me to do?
Author: admin