Past Relic - Westrak cart

Rumbling thru my old collection of bits an pieces, I came across a cartridge - its labled "Westrak" and has the model no "501 PH" plus a serial number. It also has a "JAPAN" label on it. Google came back with very little other than a commnet on a UK forum that it may have been made by Supex??? Anyody out there got any info to share on this cart?