Well I managed to get a cbr600rr shock for $140, looking at rebuilding it myself to save some coin so that would be the best opportunity to change the spring and oil thickness. If it needs to be revalved etc i might get a guru to do that.

Does anybody that has done this have any setup suggestions?

I weigh 75-80kg geared up and would prefer a firmer setup as I only use the bike for weekend riding in the twisties with the occasional track day thrown in.

I'll be installing the shock once I source a new exhaust so I can do it all at once, then i'll be rebuilding the forks to suit.

Any tips would be greatly appreciated

get it rebuild and setup by a proper specialist.

nothing worse than an incorrect fresh feeling shock on an old bike, it will feel nice no matter what compared to an old tired shock but if setup incorrect will soon throw you off when the bike gets out of trouble and the rear lets go.

you cant just change the oil weight without revalving it, that will just throw the shock off.. likewise the spring needs to be matched with the bike.

best money you will spend on the bike is getting the suspesion sorted properly.. if you ask the gurus nicely they might even help you set up the preload and stuff cheap / free after a rebuild.