The saga of the jack comes to a close.
First we nailed down the designer of these ubiquitous MCM icons, which turned to be a man by the name of Bill Curry. Then I snagged a couple modern knockoffs for a great price on the net.
Now I've gone and brought home a vintage "original". As discussed earlier, there's no way be 100% sure whether you've got an Original Curry or one of the myriad of knockoffs produced in the 60's, but the dimensions and proportions all match original spec. That's good enough for me. Done and dusted.