im 15
dont use the 283 heads they have tiny valves
i have ported and polished 283 power pack heads now and they are robbing power
get some decent heads small combustion chambers not too small or you cant run pump gas and big vlaves 1.94 or bigger
what headers (down tube size and collector size)
what cam do you have?
what pistons do you have?
have you been into the engine?