I raced a K6 600 for a while.
First, make sure the bike is mechanically sound. Fix any leaks, change the oil/filter/coolant, and safety wire anything that holds fluid or that you wouldn't want coming off.
Second, invest in a brand new stator, reg/rec, reg/rec relocation kit, and battery right off the bat. It will save you a ton of headaches later on down the road.
These bikes need to be raised to handle well at speed, so you will need a shim at the rear shock and fork extenders at the least. I had an Öhlins TTX rear shock set anywhere from 323-328mm eye to eye depending on the track, and an Öhlins 30mm cartridge kit up front, with the Öhlins fork extenders, and I would run anywhere from 2-5 lines showing on them, again, depending on the track.
Get good case covers for both sides. I like the Woodcraft ones.
Get a good 520 chain, with a host of different sprocket sizes and a bunch of master links.
Clean the calipers and pistons, and then get good race pads (Vesrah S-RJL are what I used), good braided brake lines (I ran both Galfer and Speigler, both worked well), and bleed them really well with high quality DOT4 fluid. I like Castrol GT-LMA fluid.
Vortex rearsets are key, as well as good clipons, be they Vortex, Driven, or Woodcraft.
For bodywork, get Armour Bodies. They crash well, and are easily repairable with basic fiberglass knowledge.
As I think of more I will add to it, but in the meantime, here is a link to my K6 600 race bike build: https://www.gixxer.com/forums/33-gene...ning-long.html