MIke, have you priced out how much $$$ it takes to have two manifolds Extrudehoned? By the time you pay for the cast iron manifolds, have them hogged out via Extrude, angle mill them, and then have them powdercoated, you could probably have custom headers made for the car--ouch, Baby!! Reason why I piped in here: I originally bought the cast iron manifolds for my engine, but I found cracks in one side AFTER I bought them used so a return was not an option. I finally broke down (figuratively but almost literally) and bought the Summit block higgers which I have now powdercoated like Dan Juday's. They are lighter, tighter, and look like a fighter As far as noise is concerned, I think the mufflers are a better place to concentrate to quiet the car. If Sandersons or some other high quality brand are made available USED to someone in this situation, I would certainly recommend they buy those for the better quality and sealing.
Davy