The iron exhaust is a mistake, it seriously compromises what you can do with a cam - the exhaust needs to open earlier, but less overlap. You can make a much better non-tubular exhaust from weld-els, but it's a lot of work.
If you really need to run them have them ported by Brzezinski or Extrude-Honed (both $$), and add extra thick manifold flanges between the manifolds and the ports.

I don't care what someone thinks I have on my engine, because opening the hood at Dairy Queen isn't my purpose... but that's just me.