Thanks Jeff, neat pictures.
There were all kinds of Ford (and Shelby) performance and racing parts that never got into what you might call the mainstream. Four bolt main HP289 engine cylinder blocks, single over head cam HP289s, racing intakes and carburetors made in quantities of a few to less than twenty, custom oil pans, custom exhausts, special racing starter assemblies, experimental blocks and cylinder heads in 260 and 289 sizes, and on and on. I have the fourth of five known prototype 1967 Shelby Mustang Group II induction systems. It was not something you could just walk into a Ford dealer and buy. At least one of the mid 1964 prototype R-3259 carburetors used in GT350 development still exists and is in use in a GT350.
Even paying attention since the 1960s there are some parts, especially related to Shelby American, that I have seen less the six of ever in any condition.