Unfortunately, Coversions happen.... especially alot during the early '90s... I saw many, many games converted into Street Fighter II's as well as Mortal Kombats, for quick profits. I saw them everywhere... lots of Defender & Centipede SFII conversions. Honestly, many of the games I played new were conversions, a good example is Ghosts N Goblins, I played it on an obvious Zaxxon cabinet, I never seen a dedicated unit.
