I suppose the cam timing could be played with a bit to compensate for the less than great exhaust system. I've never gone down that road very far, but I suppose someone has. The little bit I played with it seemed to be counter-intuitive. I assumed the cam would need more exhaust duration to make up for cast iron manifolds but the opposite appeared to be true. As far as I could tell, leaving the exhaust open too long just pushed more exhaust back into the cylinder. The best cam for my old manifold engine was a single pattern. The split pattern cams with more exhaust duration all had less torque. This was not a "perfect" test since I changed a lot of cam events at the same time, but it did make me think about it.