I'd bet my last pair of underwear and risk going commando the rest of my days that it wil make the needed vacuum.
As long as the engine is in good shape, and he has not done something very foolish with cam selection, it should be fine.
I too have 4 wheel discs. Fronts are early Chevelle (ECI large brake kit from Fatman), rears are Caddy calipers with built in handbrake. I have an Anglia, small block Chevy, T-5, car is light in weight, When master choice came up, I too spoke with Ralph. He advised a booster, but after speaking with him he agreed to sell me a manual master 15/16" bore. Pedals are manual brake '83 Firebird. All works very well. I could take measurements to find the pedal ratio if you like.
Ask Ralph about one of these for your system; http://www.ecihotrodbrakes.com/universal_brake_***ist.html
I would suspect that this is quite pricey, and pretty does the same thing (other than being a dual) as the Mico "forklift" cylinders that used be popular ages ago. Both will result in initial "soft" pedal travel; which is uncomfortable for a lot of people.
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