I had this discussion with my machinist years ago when I was rebuilding my 6.9. My heads needed to be resurfaced and they couldn't do it in house due to the hardness of the pre-chambers. One option was to outsource to another shop and who knows how long that would have taken. The other option was to use a set of heads they had in stock.
They were all ready to go (hot tanked, magnafluxed, rebuilt, new guides, etc) however the original owner of the heads concluded they cost of custom head bolts was too high and abandoned the idea, leaving the heads with the machinist. For all I know, they may still have them sitting on a shelf somewhere. I ended up opting for the third option, which was to buy a set of rebuilt heads at $800CAD for the pair. It hurt, but I needed my truck back together.
I still have the original heads in storage in case I decide to build another 6.9 some day.