I brought up Version IV on z80pack 1.15, ready to boot images available
at ftp://ftp.unix4fun.org:/z80pack/

Do not try to use the boot code for I.5 and II with it, won't work. The
archive includes boot and BIOS source for cpmsim, that can be assembled
with z80asm included with z80pack. A C program is used to write the boot
bits then on a bootable UCSD IV system disk.

Please note that the disks for IV have a sector interleave of 1. The
disks for I.5 and II have the standard interleave of 6, so disks can't
be exchanged. The IV disks include a tool 'diskchange', that allows to
re-skew disks. Also enough UNIX tools exists for such tasks. For an
emulation using disk image files the interleave is meaningless and won't
affect performance.

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