-  substitute 'tm' for the tape in all commands
Yes, I did it, I was very careful about not screwing up things by not writing 'tm'
  -  substitute 'hp' for the disk in all commands
Yes too
  -  use hptmunix when booting
Yes, I wrote 'hp(0,0)hptmunix'
  -  do a 'mv hptmunix unix' in preparing further bootstraps
Yes, and then I removed all instances except 'unix' with the commands 'RM HP*IX' and 'RM RP*IX' as according to this site: http://gunkies.org/wiki/Installing_v7_on_SIMH (don't worry, your HOWTO as my main guide, I just used that wiki entry as a companion). Maybe should I leave HPTMUNIX and RP*IX?
  -  'make rp04' and 'make tm' in /dev for creating devices
  -  use 153406 as size for the filesystem on /dev/rp3
Yes, I was about to type 74000 but then I saw 153406 is the correct value for RP04/5
  -  copy /usr/mdec/hpuboot as boot block? 
Yes, I wrote 'dd if=/usr/mdec/hpuboot of=/dev/rp0 count=1'

So I'm not sure what's the problem. I will try it again with the shipped Ubuntu package and I will be more careful. If it fails then I will compile 3.9-0. And if it fails again I will use Clem Cole's suggestions. Wish me luck!

BTW, what version of SIMH did you use when writing your guide, Hellwig?