I think I've seen it done twice, by guys online, always with fuzzy pictures and a shit description afterwards... will take a lot of fabrication, so unless you do TIG welding or in good with a buddy who does, I wouldn't attempt it. From the start, you're looking at cutting the frame at the lower engine mounts. I think I saw pics where someone did it, they have to be lower and wider to accomodate the ZX14 motor. Then throttle body spacing is different. So essentially you would have to cut out the whole bottom half of air box, and weld in a new plate with holes that properly aligned to ZX14 TBs. Wiring, you'd have to swap over an entire harness from 14. Probably easiest to swap over the gauges and ignition switch at that point too.
Basically, tons of work, and definitely not cost effective.