Inventory of zeros of 5 bytes or more in the IIc Plus ROM

Main Bank
C1FB - 5 bytes
C4EE - 12 bytes
C5F3 - 5 bytes
C6FB - 5 bytes
C9A1 - 9 bytes
CFF9 - 7 bytes - ROM 5X switcher

Aux Bank
C572 - 8 bytes
C7FB - 8 bytes
C7FC - 7 bytes
CE00 - 512 bytes not usable (MIG space)
D3B5 - 75 bytes - Accelerator menu text
D516 - 234 bytes - ROM 5X boot
D6CE - 306 bytes - ROM 5X misc routines
DB63 - 157 bytes - ROM 5X reset
DE00 - 512 bytes not usable (second view of MIG)
F72D - 16 bytes not usable (some kind of data table)
F7ED - 19 bytes
FB3C - 196 bytes - FBE2 ROM 5X dispatch
                 - Future: classic beep
FC3C - 12 bytes
FCC9 - 55 bytes - Accelerator speeds table
FE96 - 352 bytes - but reserve 65816 vectors
                 - Accelerator enhancements

Other potential usable space:
Aux Bank
D249-D32B - 227 bytes
This is the ROM checksum diagnostic, and we currently patch around it
because it fails with the ROM 5X patches in place, for obvious reasons.
We could fix the checksum, or reclaim the space.
To patch around it in a reclaimable fashion, a the JSR instruction at
C53D and the following carry check and JSR must be patched out, easiest
by placing BRA C555 at C53D.