what needs to be changed in a 72 340 to be like a 70 340?

i have 2 72 340 engines, and i am wanting to know what has to be changed in them to make the same horsepower as a like 68-70 340?

one i have has j heads on it, and i have a friend that knows how to port, so he will be doing the port and polish on my heads for me.

i am wanting to get about 400 -475 hp out of it. any insight?