The CBR handles incredibly well; far better than the FZ6, as it should having reasonable quality cartridge forks as standard.
You'd be surprised how comfy the CBR is for long distances.
The OE rear spring is right for a 160lb rider. 11st 6lb.
Dave your shock is knackered and you need a nice Ohlins in there. I happen to have one for sale.....
You're kind of in the wrong place for an 02 but you could look here:
YAMAHA FZS600 FAZER Genuine Parts, Accessories, Exhausts/Silencers. Aftermarket Tuning & Performance. STREET BIKE
You may be able to identify the part you want from the fiches and order it too.
The dbkillers are not straight - they are curved. When you get them out you will see this. Grab the end of the inner part of the dbkillers with a pair of pliers and pull hard. You may well need to have them mounted on the bike in order to hold the silencer well enough.
There is a blob of...
I've had a few Q's asked so for all a bit more info:
I can take PayPal, bank transfer, cash, cheques or Postal Orders in GBP.
If you want to collect the shock, that's fine or I can get it shipped next day (maybe 2 depending on courier) following payment.
The spring on the shock is the...