1976 kz 900 rotor thickness and will a drilled disc from a 1980 z1 classic work?

I have a 1976 kz 900 with a dual disc brake set up I recently came across a nice pair of drilled discs off of a 1980 z1 classic they look the same but after looking closer I discovered that there a little bit thinner will they still work on my 1976?

If your 1976 KZ900 is a KZ900-A4 it would have originally had a single front disk. If someone added a second disk they may have used another KZ900-A4 disk. The single disk KZ bikes used thicker disks than those on the dual disk KZ bikes, so that may be the reason your bike's disks are thicker than those that came on the 1980 dual disk bike.

Aside from the thickness you should measure the diameter of the disks as that also may vary. As an example - on the KZ650 single disk models the disk (swept) diameter is 250mm, but on the dual disk KZ650 models the disk (swept) diameter is 231mm.
Ed

I put later model disks on my KZ 900 front wheel.
Steve