Nor sure on the sele of the seal itself if your referring to the OD, ID of it is. Just do a online search for "your bike" fork seals on google. Just make sure they say they are for your bike in the description. Might also want to replace bushings, cooper washer on bottom of fork, oring up top and the dust seals. As for oil level its a measurement from the top of the forks, with the spring out and tube fully compressed. Stock for a k7 600 is 107mm. You can range the airgap anywhere from 105mm to 125mm. Depends on how you want them to feel. ?
I'm brand new to Gixxers, but 35 yrs of motorcycle experience. You should be able to buy seals by application (year/make/model). Go get Suzuki OEM seals, never try and save money by using aftermarket versions. The savings is gone when you have to tear in to replace them, again. I would further say NEVER EVER use any unbranded/ebay special seals, or any products for any purpose. For the most part that stuff is out of China and manufactured under virtually non-existent quality control. If they ever work they likely wont for long. Ask me how I know haha. The quality of Japanese OEM is VERY tough to beat and well worth the extra $.
I would stand corrected if there is something different about a GSXR than all the other hordes of bikes I've had to do this to. This is also true for Euro and Japan made cars.