Thanks, sadly progress has been on hold for a couple of weeks as some unnecessary nonsense was taking up my time.
I did have a chance to play for a bit at the w/e but have seen the "Enter Disk 3 Side 1" when I'd not expect too, so there is some more debugging to do.
The char disk management commands use direct serial commands too and the new disk setup is fixed to drive one and issues a format command. Due to the nature of the single disk image much of the menuing text can be altered to make more sense and will permit me to reuse that to have a loop to blank the sectors instead.
So to answer your question, no, the disk image can't be put onto cart as it still issues serial commands and reads back the response to fill the sector buffer.
However, one the other issues have been sorted out with the disk image then, as I had started with the AR:City cartridge, adding routines to redirect to the sector read calls to get memory from the cart banks instead should be possible.
It would be nice to perhaps do a crowd-funding thing to back the cart ports but obviously the recent "Games for Atari: 1977 to 1995" highlights that other's copyright has to remain a consideration.