Ok, so now I have the ROM switcher installed and working. I pulled a 2.0 ROM from my A500 put it in the default ROM slot and stuck the older 1.3 ROM in the alternate. Now I can boot using either ROM just fine.
Still not able to boot from the HD (50 Mb Seagate), no matter what ROM I use... The 3.1 ROM is totally out of the picture at this point.
With the 2.0 ROM running, booted from the SupraBoot floppy disk, formatted the Seagate drive and installed OS 1.3, then ran the update to OS 1.3.2.
After that I power down, change the jumper on the SupraSCSI controller to allow AUTOBOOT and turn the system back on... Long delay, ~2min? Then I get the ROM 2.0 "Please insert OS disk"
I'm back to thinking that the SupraBoot tools aren't really setting the master boot block on the disk at this point (or whatever it is Amiga's use for that function - can you tell my history is with the PC? - don't hold it against me - I'm recovering).
If I boot from the SupraBoot disk, I can access the HD just fine. I can copy files to and from it. Heck, I can even see a second SCSI disk when I connect that (2Gb disk with 2x 1Gb partitions).
I think that something is missing on the disk itself.
I'll try installing OS 2.1 next to the 50Mb Disk, and I'll check it out with the HDToolBox utilities to see what's what... There doesn't seem to be a copy of anything like HDToolBox on the OS 1.3 floppy disks, so I assume that tool pre-dates bootable HD's?
Is it even possible to boot an OS 1.3 system (with 1.3 ROMs) from a Hard Disk?
I'm fairly certain that it IS possible to boot OS 2.1 (implied by the "make bootable" option in HDToolBox on the Install disk).