I seem to remember a dual Hydrovac setup on some motorhomes from the 70's and 80's. You might consider plumbing your system like the newer "dual diagonal" brake systems that apply one front, and the opposite rear brake with one master cylinder reservoir to minimize mismatched braking effect between different-sized wheel cylinders front and rear. That setup also allows at least one front wheel to continue braking even if there's a catastrophic failure like a blown wheel cylinder or burst line on the other system. Since front brakes do the majority of the stopping due to weight transfer except in max-payload situations, it's a good idea to keep at least one front brake capable of functioning at all times.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!