Roland GR-300 polyphonic guitar synthesizer SN 284090

via this auction

"Vintage Roland GR-300 synth pedalboard in working condition, tested with a Gibson SG and a Roland GK-1 with 24-pin cable. This unit will work with a Roland G-202, 303, 505, 707 or 808..."

Note the 303, 404, 707, and 808 are references to the corresponding G-303, G-505, G-707, and G-808 guitar controllers, not the TB and TR models. :)

Original box for the GK-1 Synthesizer Driver pictured.