I erased the hard drive and started over just as outlined, but same result--all partitions (including Sandbox as well as normal backup copies) are non-OS 9 bootable. However, I have a 3rd hard drive (Maxtor) for which this worked. In fact, on that hard drive I used Erase Then Copy yet it is OS 9-bootable. Could the Hitachi drive somehow be non-Mac OS 9 compatible?
Also, I found an easier way back from the dreaded 3.5" disk image with a blinking question mark: Just hold down X (for OS 10) while booting. That forces an automatic reboot which then boots from OS 10 on the parition from which I was trying to boot OS 9.