Great post, Dave!
Lots of good information. For those interested, here's the California Stainless Manufacturing site. Lots of great darkroom equipment. And here's a page describing their gaseous burst hardware (no prices, though). Their timer is shown at the bottom of the page, along with a mention of their one-gallon plenum.
And somewhat off-topic, but probably also worthy of mention, for everyone who thought that low pressure sodium vapor darkroom safelight illumination went extinct with the Thomas Duplex, here's their OC-1012 Sodium Vapor Safelight - a similar-design look-alike of the Duplex.
I may look into that ready-made Arkay-compatible one-gallon gaseous burst tank you mentioned.