I know this is OLD, but figured he still has the game. I think you can use ANY Mortal Kombat 1 sound card on ANY MK1 main pcb board. I have 3 MK1 sound cards and they all work on a T-Unit version 4.0 main pcb board I have and 2 of them are SLIGHTLY different in design, but all work fine. Same cables attach to same connectors on both types of these sound boards. I also have a "new-to-me" dedicated MK1 I just bought and it has the Y-Unit main pcb board (version 4.0, too). I can check those sound cards with the Y-Unit board if you need to know if they work with it.
Good luck!