Man... Frankenstein.
Haven't heard that tune in ages. da dat, dow, da, dat dat, dow'dn dat, da dat, dow'dn dat.... doodendoodendoodendooda....

I know he used some of the first keyboards that had pegs suitable for strapping around the neck... like the Korg Poly800 (got one.. woohoo).
That was back when synths used to be giant things with knobs and suddenly Korg came out with this amazing synth that was like 10lbs and could run on batteries with touch controls.
I never remember seeing a hybrid guitar with a keyboard attached though.

I'm thinkin... guitar/guitar synth on top, then a keyboard below it.
All midi'd up with touch controls (like the Roland GR808 guitar, but more modern and with way better tracking)
Wireless... wireless headphones...