They all crack within a few ten thousand miles. They aren't usually a problem until several hundred thousand miles. I was told this one had less than 200,000 miles on it.
So it'll probably be fine for another couple hundred thousand miles. The cracks are hairline, wouldn't be visible without being magnafluxed or having really good eyes really close.
That's the story for any used Cummins head. Cummins doesn't even test heads for re-use during an overhaul; they order a new one when the old one comes out. It's usually a toss-up between a used genuine $200 head or a new cheapo aftermarket head for $500 that will have its own cracks after 10,000 miles.