Via this eBay auction: a UTC A-12 mounted on a plate-retained octal plug, with the pins wired to correspond to the pin-out of an Altec 4722 input transformer.
It had simply never occurred to me that the mounting-diameter of a UTC A-series corresponded to the mounting-diameter of those octal-mount plates. Well done sir. Great idea if you have an Altec 1567, 1566, or ANY piece of old pro audio gear that uses octal transformers – and a great many do. RCA, Newcomb, Ampex, the list goes on….