Balmar can likely configure a kit, I've done a number of them, but you will need to take specific measurements of the crank pulley & water pump pulley as Universal shipped the M-25XP with multiple different pulley configurations. Universal had a huge lack of consistency during this time frame. Unfortunately this engine is not just "order by part number"..
I can get you through this and depending upon your specific configuration may be able to come up with a solution: compassmarineservices AT gmail DOT com.
This is an M-25XP with Balmar Serpentine kit and 120A 6-Series...