I wrote another Z80 boot loader, boot-rel.z80, that relocates to FF00H and
then initializes page zero as later CP/M versions do. With this one can
run CP/M 1.4 ddt on the system and inspect memory and such. The bootable
1975 CP/M disk includes this boot bits.

Enjoy,
Udo Munk
--
The real fun is building it and then using it...