I'm not exactly sure (because I don't own an older style 26.75 kettle) but I believe that the Gourmet BBQ cooking grate from a new Weber Summit charcoal grill just might fit on an older style 26.75 kettle.
I have a newer style Weber 26.75 kettle and I also have the new Weber Summit charcoal grill. I tried putting the cooking grate from my new SCG into my 26.75 kettle and it was slightly too small, which means that it just might fit the older 26" kettles because those cooking grates sit lower in the bowl because they are a smaller diameter. If anyone with an older style 26" kettle can tell me the diameter of the cooking grate, I can immediately tell if it will fit or not.