cleaning up the slant six head

Dykem (or Sharpie :thumrigh:) around all of the ports, align the gasket and gently scribe a line at each port on the head around the gasket's opening. Open up the intakes to the scribed line. Open up the exhausts to within, I dunno, ~3/32" of the line (smaller). Blend all ports down 3/4"-1" into the head.
The idea in the step on the exhausts is to create an Anti-Reversion (AR) feature. Can probably devote a whole thread just to discussing AR, but the OE's have done fairly well w/o paying it much attention.

Alternately can open up the header or exhaust manifold bigger than the gasket opening and bring the exhausts to the scribed line, but given the RPM range you don't need every extra CFM that you can squeeze out of the ports and keeping the port velocities up is more important than gross flow. though I'm doubting that the difference would be huge, it is less work to put the AR feature in the head and leave the exhaust manifold/header alone..