For anyone who cares, this is what I had asked in my thread:

> 
> The question itself is tricky for the vanilla user: has anybody here turned a
> non-multi-lib distro to a multi-lib? where there any apparent issues? and has
> anybody done what I am trying to do? Which distros are multilib when vanilla?
> 

Slackware (my distro of choice) is not multilib when installed 64-bit vanilla.
(There are some good reasons for this having to do with avoiding redundancy.)

I decided to do two tests. I completed the first and thought I'd report back.

Success! I took one of my VirtualBox installs (in a VDI file) and added a new
VDI "drive" to it. I "rsync-ed" all of the relevant directories from the root
filesystem / to the newly added drive like this:
'rsync -av  bin sbin root run var usr dev .... /mnt/tmp'
(the /dev/sdb1 is the new VDI and mounted under /mnt/tmp)
Then I edited the usual places in /etc/fstab to get the "/" to be atteched to
/dev/sdb1 and edited LILO (that is what I used here) to boot from /dev/sda1
as before but point to /dev/sdb1 for the root directory. Nothing new here, and
this would make no difference. I essentially replicated the system to a new
drive with the expected success. Then, I added the packages from "alien" from
Slackware with the "installpkg" installer (what "apt-get" is for Ubuntu) and
ran through the appropriate steps. All worked as expected on the 64-bit side
and I have no plan to test further (I tested 3rd party dev. software too).

I will do the same on my main system and then test 32-bit runtime and code
development on that. That is step two. Will report back.

So far my impression is "seems too easy" and I want to test further before I
commit.

I hope you guys find it useful. WINE users may want to monitor this thread.