Hello fellow Graflexers,
After a fair amount of research yielding nothing about the specifics of the Super D's flash-sync, I investigated the camera, and have now successfully used it with electronic flash.

So, to help everyone else who might wish to do this, I compiled a blog including pictures of the mechanical components of the shutter:

http://tobiasfeltus.com/blog/2012/x-synch-on-the-graflex-rb-super-d/

I hope this is helpful to others.

Keep shooting,

Tobias