in the pictures of the head porting i noticed that your diesel valves are slight square or they look like a hockey puck.whats up with that?in gassers they have aerodynamic shapes to ease the flow and get extra CFM's.also you are right that that manifold was restricting your power. manifolds with a hole like that would only feed the closest cylinder and not the others.but what if you had multiple inlets on the manifold you could get equal boost across all cylinders.also watch out in tuning your inlet runner length!in gassers a short runner is  good for high rev's but a long runner is good for low down power.motorbikes have adjustable runners with a motor controlling their lengths fr both high and low rpm power!