Kawasaki had a problem with liner distortion caused by pressing in pre bored sleeves, hence the high oil consumption on some of the GPz1100's. A rebore oversize or a used servicable block is your answer. 550 mills are pretty cheap.
I read somewhere that motor manufacturers buy in pistons for several dollars each, I doubt if kawasaki pay even cruising image prices.
Remember cast (oem) and forged (wiseco) run at different clearances, also the block needs to be bored individually to each piston size and numbered. So putting better pistons in later will involve a new rebore. Ask the borer to champher the bottom of the liners, the standard bores have quite a generous lead in, at 61mm the liners are pretty thin and a broken ring and scored bore will really riun your day.
I did consider GPz305 2nd oversize pistons to make a GPz630, maxxed out without a big block conversion.
The ZR550 block has bigger cooling fins, that might be worth chasing.
1980 Gpz550 D1, 1981 GPz550 D1. 1982 GPz750R1. 1983 z1000R R2. all four aces
