I second what xb33bsa says....if the fork offset is enough to counter-act the difference in length, keeping trail where it should be....the fitting of a wheel is "simple" but for sure not the cheapest endeavor.
for starters, the brakes on GSXR's are either 320mm or 300mm, depending on the year and model. the rotors are generally 5mm or so, some 4.5mm thick.
A honda/comstar is going to have I think 280 or 290mm rotors, 7mm thick. the offset from the centerline of the wheel will also be different. All of these issues can be taken care of with a rotor adapter that bolts to the wheel, sets the correct offset, and bolts on the proper rotor.
for axle, you have a couple options. If you want to retain the comstar speedo drive then you have to build a custom axle and spacers. I did all of this for an xs750 so I'll show you how I did it.
stock axle below, my axle above and spacers above (converts 17mm axle to 30mm axle mounts)
welded a "L" tab to the loose spacer so once pinched into the fork lower it holds the speedo drive as the stock fork did. The length of the sleeves on the custom axle double as the spacers to center the wheel.
and how I dealt with the rotor problems