Hi Neal ... We have success.
I automated the transfer and write to disk, using BASIC to get the track sized chunks (I have added a hardware handshake feature to my serial port) into a RAM buffer then wrote to disk as you suggested with a machine code subroutine.
After a couple of false starts, (a bad floppy disk and a program bug) transfer to disk completed.
I skipped step 3 and instead swapped the NAS-DOS roms for the POLYDOS3 boot rom I had blown earlier and booted up.
The "Boot which drive" prompt appeared,I pressed 0 and off it went.
If you would like a copy of the disk I'd be happy to pop one in the post for you.
Cheers
Andrew.