Whew...it turned out to not be as bad as I thought...hopefully this will help anyone else facing the same issue.
After my original boot disk was converted to "Dynamic" from "Basic", there was no easy way using Windows' tools (e.g. diskpart.exe) to revert to "basic". However, I didn't have to.
Using diskpart.exe, I removed all the partitions from the new disk ("disk 1"), using:
diskpart> select disk 1
Using the Disk Management console, I then mirrored the "system reserved" partition from Disk 0 to Disk 1, and then mirrored the "C:" partition from Disk 0 to Disk 1. I then allowed the mirror to fully re-synch.
I shut down the computer and rebooted using "Secondary plex" (Disk 1) to confirm I could boot from the new disk. (I could)
I then shut down the computer again and removed Disk 0 and confirmed I could boot from Disk 1 (I could).
I then removed the mirroring on the two partitions and rebooted one more time to confirm the settings.
Finally, I used msconfig to remove the original system location on Disk 0 from the boot record, and now I can boot from the new disk as if it was the original system.
Lastly, I reconnected the original Disk 0, which still had a "D:" partition on it I wanted to preserve. When I rebooted and opened Disk Management console, the original Disk 0 showed up as "foreign disk" and did not mount, but the three partitions ("reserved", "C", and "D") were still there. I was able to "reactivate volume" and remount the original disk, so I cold continue to use the "D" partition or do whatever else I needed to do with it.