|I never knew what this Will Clark card was.|
In the intervening years, many resources have come online. The back of the card indicates that it is card #9 in a 1988 set called Big League All-Stars Series 2. Thanks to The Trading Card Database, this is enough information to track it down. I can say now that this is from an unlicensed set by Pacific Cards and Comics. I can't find anything else about Pacific Cards and Comics, but knowing this much is a victory.