Try,
this:
Code:
sudo find {/var,/opt} -type d -iname \*package\* -user root -exec ls -l {} \;
It will list down all packages you have installed.
Since I have no idea how it is arranged under lfs I cannot point out which folder are your packages are kept. You may try look for it from /var, /opt or even /tmp. In Slackware it is located at /var/log/packages/records-of-all-packages-installed-here.
Hope that helps.
Good luck.