According to the writeup on Joel Nystrom's 67 GTX in MuscleCar Review last month, He reportedly runs heads that have been custom ported to flow 420 on the intake, and 315 on the exhaust.... (at this point I would ask you to do the math on that relationship).

The same writeup notes that he employs a camshaft that features 4% more duration on the exhaust side. This makes sense, since his hemi runs 1250 cfm worth of dual AFB on the intake side, but stock exhaust manifolds on the exhaust side.