Dunno if anyone is still considering this shock conversion anymore, but if so I have a small addendum.
As mentioned a year or two ago, I found that it
is possible to fit one of the earlier 2006-07 R6 rear shocks to the FZS600. This is the shock with two separate top adjusters (anodised gold and blue).
The advantages are:
1 - It will not fit the Fazer FZS1000, meaning: 2 - It is usually unloved and unsold on ebay, not to mention generally cheaper.To fit it to the FZS600, the same conversion parts are needed as per detailed on this thread, but you also need to file a tiny amount off the top of the shock to get it to fit, as per picture below. This groove on top stops it from fouling the frame's crossmember above the shock. There was no point in taking a picture of it in position as frankly you couldn't really see the interference between shock and frame.