Epilogue:
Engine has 30 hours on it now. 25 hour oil change was clean, with the exception of what appeared to be some blasting media in the filter. I thought I had everything pretty clean, so I was surprised when we found some of this stuff at the 2 hour change. It looks like some stuff I noticed in the exhaust ports, so I assume it was hiding down in the heads somewhere. Concerning as it has to go through the oil pump to get to the filter. We stuck a borescope into the sump and found a little bit in there too, which we managed to flush out with mineral spirits. I'll change oil again at 50 hours and hopefully it will be gone.
Otherwise it's running beautifully. It burned 2 quarts in 25 hours, so I'm considering break-in complete and switched back to Phillips XC.
I sent the my crankcase cores back to Divco in mid march, with radio silence since. Because it's about $6500 hanging out there...I decided to call and check up on it. They show them as received 3/24. Apparently it takes 60 days to "get through inspection". Sigh.