I poked at the rom with a hex editor. According to a gamefaqs item guide that datamined the object data, I imagine it would be fairly easy to reverse engineer the monster data and make cards a fixed drop.
You could go a step further and randomize drop locations, or even dss effects. Eg 0,0 is the fire whip, 100 is the skeleton transform. But who says you couldn't change the mapping and end up with eg Venus and Serpent summoning a cockatrice?
Throw in a rebalanced leveling mod and youve made it great again