Mill rotors thinner and cross drill them?

Yes, 260mm gpz550 zx rears on the front with Nissin multipots, and a 260mm zx550 front disc on the rear. Rotors are flat, not dished so offset isn't a problem. Not ideal, but will work. I'd have preffered to use bigger 280mm zx1100 discs as I did on my other 550 build.

The LTD 1000 had thinner rotors than the Z1. I have LTD discs bolted to my Z1 (74) rotor
hubs which I cross drilled. They have been on the bike since 1980.. I had Mark Zero Rotors for about a week or so before they started warping when hot.

Mac, you don't mention what year / model bike they are going to be used on, you may be able to get some Factory drilled discs from another year / model bike , that will work & be safer than taking away the integrity of your sold discs
I replaced my stock discs with factory 78 Z1R discs on my 80 LTD 1000
stock discs

Z1R discs





Pete

As far as I can tell, the Z1R disks and the disks on the LTDs are exactly the same, except they have different hole patterns. I have often wondered if anyone has shadily gone into business buying blank disks off of KZ1000s and KZ650s, drilling them in the Z1R hole pattern, and then selling them on Ebay as the genuine article. Z1R stuff pulls crazy money on there, when often the same parts can be found on other models.

pete greek1 wrote: Mac, you don't mention what year / model bike they are going to be used on,

It's not my bike...but I believe the guy (by his flare on Reddit) is running a KZ650.