Dual master cylinder update

[V8 Bob]

37 Cab,
I am very familiar with dual master cylinder operation, mandated since '67. The output pressure will equalize but at different volumes of fluid. Re-read my previous post.
You are simply wrong about wheel cylinder sizes. The fronts are always larger than the rears on cars and light trucks, because the fronts do most of the work. That rule gradually reverses as vehicle weight increases in med/heavy trucks, RVs, etc.
The fact is your plumbing is wrong, and could be dangerous, because the loss of the rear circuit could result in marginal (or no) front braking due to insufficient fluid volume.