Cosworth used to make a 8something and a 9something kit for the 88-89 GSXR that would fit the Kan-o-tuna's as they are the "short stroke" motors with low end cams in them. I have the 8something kit from my 88 in the garage somewhere.
There are three different 750 oil cooled blocks. The original 86-87, this block has thinner casting and when we do the sleeve type kits, we can only put the 907 in this block. Then there was the large bore short stroke J 88-89, then they went back to the long stroke but the block is thicker. This is the block you have to use to do a 955. This is the block that the new Wiseco kit is for.