I found sources to a BSD4.2 hacked version of (SEA) arc utility from 1988.

But instead of porting it, does anyone know of a ARC extraction utility to
use? (The old source seems to have different syntax for scandir and
alphasort.)

The .arc files (from a floppy I made in 1989) I want to look at are:
 ARC archive data, dynamic LZW
 ARC archive data, uncompressed

Thanks,

   Jeremy C. Reed
   http://bsd.reedmedia.net/