Single to dual M/C. Some specific queries

The newer distribution block does more than "detect" a difference and turn on a light. In the event of failure, a metal "piston" moves in the failure direction and blocks any flow....
Thanks for the info. Is the distribution you refer to actually a proportioning valve, or just an uprated distribution block?
I was under the impression that the dual master cylinder provided sufficient circuit protection if one side fails.
I’m here to learn. If I keep my existing block does anyone know what size plug is needed to block off the rear port as I need to find that?