To know which package contain which files you could parse slackware/MANIFEST.bz2, actually, you could recreate all packages "logs" by parsing slackware/MANIFEST.bz2 correctly and adding the info from the .txt files that corresponds to the package (I don't know if the package size and location shown on logs are important, I think they aren't).
I don't have time these days, but if you still can't do it at the weekend I could give you some help with it.
From MANIFEST.bz2 (I took some lines only..):
|| Package: ./a/aaa_base-10.2.0-noarch-2.tgz
drwxr-xr-x root/root 0 2005-09-10 15:40:48 ./
drwxr-xr-x root/bin 0 1997-10-06 01:10:09 bin/
drwxr-xr-x root/root 0 1997-10-06 01:10:09 dev/
drwxr-xr-x root/root 0 2005-09-10 15:40:48 etc/
drwxr-xr-x root/root 0 2001-02-05 17:47:32 etc/X11/
-rw-r--r-- root/root 17 2005-09-10 15:40:48 etc/slackware-version
The log at /var/log/packages/aaa_base-10.2.0-noarch-2:
PACKAGE NAME: aaa_base-10.2.0-noarch-2
COMPRESSED PACKAGE SIZE: 8 K
UNCOMPRESSED PACKAGE SIZE: 80 K
PACKAGE LOCATION: /var/log/mount/slackware/a/aaa_base-10.2.0-noarch-2.tgz
aaa_base: aaa_base (Basic Linux filesystem package)
aaa_base: Sets up the empty directory tree for Slackware and adds an email to
aaa_base: root's mailbox welcoming them to Linux. :) This package should be
aaa_base: installed first, and never uninstalled.