It is apparent that one of the issues is that the engine is starving for air. Port matching the intake to the heads along with the correct intake gasket will help it to breath. 850 cfm carb with a carb spacer will help also.
I run a roller 340 with ported X heads and matched AirGap intake, 800 cfm carb and it pulled 442 hp with a smaller cam than you have.
The guy who did my porting wont even touch your heads unless you give him the intake and the gaskets you are going to use.