Hi Muddy,
I was running 91 GSXR750 38mm CV on my 1260 and they have round inlet (filter side) not the ovalish type. I used GSX1100 rubbers but new so they would stretch over and standard airbox with the inner metal ring removed again to aid fitment over the larger diameter. My engine had dialled in cams.
These are identified by the side adjuster for idle speed, they are shorter than the 1100 34mmand I had to cut flush the bottom drain tube so the airbox could sit forward.
Cheers Andrew.