Couple of points.
Script released by RL has a bug in it for Left Upperarm.
Biceps morph is flexing with Forearm rotation by X axis which has the same sign for both arm. No problem here.
Deltoid is driven by Upperarm on Z axis which has an opposite sign for Left/Right arm.
But the routine for morph value calculation is the
same.
For
003_left_deltoid_muscle it has to be
1+angle_z/90 (instead of
1-angle_z/90).
Generally it's not that hard to write a script for JCM.
The problem is to apply all those morphs to the character in the first place and make them work efficiently.
There is no one click morph application to the character, no profiles and they are cannot be transferred between characters.
Remember that any individual cloth mesh on character must also be driven along.
Meaning adding/removing/replacing cloth would immediately invalidate existing morphs
Years back RL has tried and failed to produce a viable solution for automation of JCM.
To succeed It has to be developed on very much different level - other than primitive mesh morphs and Python scrips.