Pulled the camshaft off and started sanding the head surface.
The small gouges look better, but some others are a small concern. I think copper sealant should resolve those issues.
This one is odd: it sems to have been partially milled off-axis...
I got a 7x24 tempered glass shelf at the store and taped the 600grit to it. I lubed generously with wd40 and slid the head back and forth longitudinally.
I'm not sure I want to sand any further... The straight-edge currently shows no gap end-to-end and corner-to-corner, but the openings of the precups seem about .001" proud. If I keep sanding, I'm concerned that the precups, which are harder, will let me rock the head back and forth on them and create a rise, since there is no way for me to force the head to maintain the same plane as the glass.