Thank you, chef!!! Worked like a champ!
For any other semi-noobs (like me), put the tsdnwin.exe file in C:, got to Start>>Run, then type:
C: sdnwin.exe -nocheck
Though I then learned that my drive didn’t like the “no region” RPC1 setting, so I had to create another patched firmware without that option. Now all seems to be grand.