I know back in the day G&L HBM spindles were nitrided. They were suspended vertically in a nitriding chamber that was installed in hole in the floor. I was told it was 75 ft. deep to allow long box way sections to be nitrided vertically as well.
The hardened box ways were installed in scraped cast iron machine frames then bolted in place. That's why they were called "replaceable hardened ways".
Dick Z