I just did a quick mod on a Soul Edge board to change it from JAMMA+ to JAMMA. Modification eliminated the need for the kick harness.
Here is the important parts of the pinout that you will need.
This is for the secondary edge connector.
Solder side
pin 5---key
pin 8---player 2 button 4(guard)
pin 20--player 1 button 4(guard)
Simply solder wires tagging thos locations to the Button4 locations on the standard Jamma pinout. I also cut the traces on the JAMMA side, just in case.

Top of board. Note, the solder you see on the secondary connector in this picture is not needed, that is the result of me magically soldering up the wrong side of the board!!!!!!!!!!!!

Bottom of board. Tape keeps the wires from getting ripped out.

Block buttons now work without the kick harness. See, both players are blocking.

Time to play!