Nathan - The 1951 and later style underbed spare tire mounts are pretty readily available. Not hens teeth (or priced like) the earlier style slide out type.
No factory in-bed units, but it wouldn't be hard to fab up something I think.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)