Thanks to comrade Phillip from Los Angeles, who suggested I investigate Bunker Guitars. In 1955, Dave Bunker patented the Duo-Lectar (which the kid in the picture is playing). It was a double neck guitar played by tapping the strings against the frets - just like every poodle-haired metaller would do thirty years later. Dave (who is, inevitably, from Washington State) is a guitar maker who played with Elvis and Johnny Cash, although "One of Dave's more enjoyable experiences was entertaining on cruise ships". He's still making Touch Guitars, and will sell you a double-necked guitar/bass guitar for, er, $4,395 (that's a factory direct bargain!). And, of course, Ed Roman, has one in stock - once you've got past that lime green fretless monster at the top of his page...