OK, an update. Back on Feb 19, I mailed both heads back to SoCal at their request. (SoCal paid for return shipping, and received them Feb 23.)
SoCal examined the heads and determined it was a casting defect at the seam on a driver's side head intake runner, and they offered to replace the head, since they had provided the cores.
Today (45 days later, or 53 days counting shipping), I got the original passenger head and a new driver's side head back.
I had ordered new gaskets, etc; the injectors are back from a tune-up at Exergy; and I'm set to put everything back together this weekend!
I have my dad flying out to help, and with any luck, it should be purring like a kitten again by Sunday! Then off to Idaho Rob to finish up the tune, and finally I can tear up Firebird Raceway and see what she does!