Thanks all, I've been advised both the rear shock and front springs haven been upgraded to yss ones. I'm quite happy with the purchase if I do say so myself, I will take a peek at the headstock for a stamp. Failing that I will just pop the sprocket casing off and take a peek. Better safe than sorry as I have read a few horror stories on here about the sprocket coming off and causing some expensive damage.
I noticed the YSS sticker on the swinging arm, and as far as I know they are only available when purchasing a YSS product, it would be interesting to know what has been done to the front forks upgrade wise. YSS are manufacturing the cartridge fork emulators now and are available at a very reasonable price from a number of outlets Wemoto.com being one of them.
a quick glance at the rear shock will tell you if its a Yamaha pogo stick or something a little bit special. I have placed a pic of the Yamaha one in here for comparison with yours.
I hope you find it is an upgraded shock cos that will save you a big spend out.
I know Hagon do one for the FZS600 as do YSS and Nitron, I sure if you look you will see a name on it.
plus pic of emus and one of sprocket nut