One minor correction. The 900's came with 15/35 but the 1015's came with. 15/33.
Sort of... According to the FSM, the '77 A1 and '78 A2, D1 came with 15/33. The '78 B2 manual also gives 15/33. The '78 A2A manual also gives 15/33.
However, the '79 A3A, and '80 A4, D3, and H1 all state 15/35. I don't have the supplement for the '79 or '80 LTD, so I can't check that model.
Anyway, that's why I qualified my statement by saying the "
79/80 KZ1000 came with 15/35 sprockets"
One could guess that Kawasaki reduced the final drive ratio in '77 when the engine size increased from 900 to 1000, since it would have more torque. They also reduced the redline from 9000 to 8500. But then may have returned to the higher ratio in '79 due to increased market competition. It may have allowed them to advertise better performance numbers.