[nickd]

Thanks for the feedback! Using as-is is definitely off of the table. Options, barring the horsepower fairy dropping off a set of 9m heads, appear to be: weld/repair existing, replace with a new/used head, or grind off the boss entirely as long as the crack isn't deeper into the casting. The latter option sounds easiest, if only to avoid another complete valve job.

What I'm wondering about now is what I can't see. If the new guides were pounded in so brutally, are there invisible problems lurking? Are there potential problems that magnaflux won't find? And then, is it safe to grind off the bosses with the guides still installed and how delicate of a process is that?