Without X and the libs I would think apsfilter would probably be best. It should provide graphics with color capability. Apsfilter will need ghostscript installed. Both are available in Slack. Probably should avoid CUPS without an X system, but it can be managed at the command line if one is really dedicated.
If text only is desired, then I believe the 440C will perform as a normal ASCII printer. It will require a LFCR filter for proper line termination though. Otherwise the staircase effect on each line. Usually just a print filter script listed in /etc/printcap file. I think I can post an example if needed.
Also, for your reference you might take a look at this website, http://www.linuxprinting.org.
BTW: Welcome to LQ and Slackware!