Bought from Malcolm Curnin, aka Yorkshire Engine Services. Had one back in 1985 (pics) and I remember it being a fast little machine then.

Text here taken from Bonhams auctions in 2014.
FRAME NO. ZX600A 004667
ENGINE NO. ZX600AE 004501

One of the most commercially important market sectors, the 600cc or ‘Supersport’ class was created overnight by Kawasaki’s introduction of the GPZ600R in 1985. The GPZ600R featured a water-cooled, 16-valve, six-speed engine/gearbox unit housed in a steel perimeter chassis clad in ‘race replica’ bodywork, an outstandingly successful formula that would be copied by every other Japanese manufacturer within a few years. Stylish, fast (130mph), less intimidating – and cheaper – than its bigger brethren, the GPZ600R deserved to sell by the boatload, and it did. Few motorcycles of modern times have had such a lasting impact. This example was acquired by the current vendor in October 2012 and subsequently fully restored to an exceptional standard with no expense spared. Photographically documented on an accompanying CD-ROM (viewing recommended), the restoration included a full engine rebuild; frame and swinging arm blasted and repainted; new paintwork and decals; forks overhauled and polished; wheels blasted and repainted; anti-dive rebuilt; seat re-covered; all plastics and switch gear restored; and the carburettors overhauled. New parts fitted include the brake discs, tyres, control cables and all bearings. Presented in effectively ‘as new’ condition, this beautiful future-classic Kawasaki is offered with SORN paperwork, V5C registration document and recently expired MoT (August 2014.) The provision of braided brake hoses is the only notified deviation from factory specification.