Kim hit the nail on the head. You select parts based on the engine you're building. Even when planned to be used in the same way i.e. 80% street / 20% strip, a 347 would be very restricted when built with parts that are optimum on a 306.
A 347 is 13% bigger than a 306 so in theory would require 13% more airflow to have the HP at the same peak. The HP would be about 13% greater at that point on average.
People do this all the time, put 302 parts on a 351 and can't understand why it's makes only a little more HP and 50 ft. lbs more torque.
Experience is the hardest teacher. It gives the test first, and the lesson afterwards
To upset a Conservative, lie to them. To upset a Liberal, tell them the truth.