I'd put a pressure check at the very top of my list on that 2X4 intake with special emphasis on the push rod hole porosity as they run by the intake runners...many of these intakes have problems in the push rod holes
http://www.gessford.com/projects/ima...akePC-01BT.jpg
some images of the plates required
http://www.gessford.com/projects/ima...Intake-013.jpg
The heads need to be P/C'd also....I think you'll find the problems.
George