Ok, that makes perfect sense.
Ok, so with Interword removed, I have MMFS at slot 15 and Basic at slot 11.
Ok, so It seems that whatever slot I put Interword in, it shows up in slot above BASIC in slot 11. I suppose I could dump the MMFS ROM and reburn so BASIC appears ahead of MMFS.
The Interword ROM is on a daughterboard with some sort of IC (GAL/PAL maybe) and won't work off it. It always appears high up, and in fact shows in multiple slots when using RTOOL.
I can drop out of Interword by using the :kill command to drop to the * prompt, then typing BASIC, or I can press SHIFT+BREAK to force a boot from the disk inserted into the MMFS disk 0.
I'd really like to keep Interword as it came with the machine and has some sentimental value, but unless I use the original mask ROM, it seems to become the language ROM with the highest priority.
Any suggestions welcomed