Thanks to all who replied!
I never got the setup installer to complete, but thanks to lleroy I now have the system working!
The method was simple in the end:
First mount the target and source partitions (while booted to installer as before):
mount /dev/hda5 /hda5
mount /dev/sda5 /sda
Repeat install-packages for desired package series...
This gives you the installed base, but lacks fstab, host and network params, etc...
You cannot simply chroot into the resulting tree and configure lilo because there are no /proc, /dev entries yet, so I added a stanza to the lilo.conf that I am using to boot the installer kernel - voila! I can configure native lilo later, install to boot partition and chain from the MBR. Easy.
I had to create an fstab from scratch, but since there are no CD/DVD drives and I initially installed everything to one partition this was easy:
/dev/hda5 / ext3 defaults 1 1
I then chrooted into the target and used passwd to set the root password and used netconfig to set up a few things. Grabbed a copy of my master hosts file from my network... rebooted to new install!
To make the story complete - I am using the box as a headless server so did not install KDE, X, and quite a few other things. I will clean up the other partitions that I used for the installer, remove the DVD tree, and add them to fstab for usable space. I will leave the gparted and Slackware installer boot options intact for future use, but they reside on a small partition that is otherwise unused.
Another box saved from the landfill, and a very valuable addition to my currently limited resources! Thanks to all, and a special thanks to Pat who has made it possible for me to turn lumps of lead to gold when needed!
Now I need to clear my stuff out of the kitchen before my wife strangles me with a piece of cat-5 cable... she has been very patient...