On Wednesday, January 22, 2020 at 10:26:40 AM UTC-8, John Foster wrote:
This has gotten me thinking then: is there any reason one couldn't use a standard "yolk-style" primary regulator for the oxygen tank?...

The big reason is that at a lot of places you need a medical prescription to fill what looks like a medical bottle. With a CGA540 you can get a fill at any FBO with O2, or at any welding gas supplier.