So, the CE drive mounted on my 1400, but I could copy only small files to it without there being errors (-39). I opened the box and put a tested 1GB drive in it, freshly formatted to HFS standard. It mounts on my 8600 and I copy some files over. Then on the SE, it looks like I am going to boot normally for a few seconds and then I get a sad Mac screen. I turn off the drive and reboot, and it starts fine.

It seems that between the SE, and OS 9.1 on my 8600, that there are some significant differences with regards to either formatting or termination.