Gibson 1964 Guitar and Bass catalog. Page 15. The Gibson special order instrument department, situated on the top floor of the main Kalamazoo plant, was responsible for the high end jazz guitars (see pages 2, 3 and 4) but also the double neck instruments shown here. They were only produced in small numbers and had to be specially ordered.
Although solid-body double necks had been available since 1962, this was the first catalog to picture one. Prior to this the instruments were spruce/maple hollow bodies. See the 1962 catalog.
This catalog page details three models, the Double 12 (EDS-1275), Double Mandolin (EMS-1235) and Double Bass (EBSF-1250) doubleneck guitars - although other combinations were possible, most notably the guitar / six string bass made for Elvis Presley for use in the film Spinout more.
Prices for the EB bass series in 1964 were as follows: EDS-1275 $685, EMS-1235 $685, EBSF-1250 $765. (US zone 1 prices)
$12000
$13499
$54900
$11000