Earliest KS I've ever seen is 1.1, but why would you want to use it anyway?
1.2 & 1.3 are a lot more useable. I've got original KS disks 1.1-1.3 if you'd like one. Otherwise, grabkick or some other KS utility found on Aminet could make an image of your older Kickstart out of an A2000 or A500 - to which end, you'd be able to simply copy over to a disk for the A1000.
There's also a utility to throw both Kickstart 3.1 and 1.3 on the same disk. Just do a search for A1000 and you'll see it....