You should be able to get the proper jetting for that setup with the original carbs. It takes some work and trial n error testing but thats going to be the case no matter what carbs you go with.It's running straights pipes without mufflers & the air box was revoved & it's running with 4 pod type air cleaners.
Your bike, if stock, has 26's on it already. 1977/78 KZ1000's had 26 Mikuni's and they went to 28's in 1979. The 26's from a 1976 KZ900 should be fine.Just purchased this bike & it's becoming a money pit. Needs carbs & am wondering if 26mm carbs from '76 KZ900 will work.