You know, there were many, many multi necked guitars out there; Paul Bigsby - of the trem bridge fame - was also a skilled luthier who made double and triple necks for country players in the 50s, which are exceptionally valuable and quite well regarded these days!!

Check out Pat Methenys' Pikasso guitar, or Rick Wakemans' Wal triple neck. Steve Vai has an Ibanez triple and John Paul Jones used an Andy Manson triple in Led Zeppelin while I saw Jimmy Page with a triple on a Page/Plant tour.

Doublenecks are reasonably common with - off the top of my head - Malmsteen playing a 6/12 Strat and Mike Rutherford using many different doubles; Allan Holdsworth uses a Steinberger double and of course, Geddy Lee and Alex Lifeson from Rush both used doubles in the late 70s/early 80s on stage! My personal favourite is Dave Mustaines VNMT Vee.....

It seems that quite a few of the multis built early on for for the C&W type crowd, and most featured mandolin necks sprouting from the upper bout...

They fascinate the living daylights out of me and I am trying to find out as much as I can about them; it would appear that the golden age of multi necked guitars was the 50s, however, with most luthiers offering doubles as a matter of course.