Disc Brake Hold Off & Prop Valves

AJ/FormS said

I rundisc fronts/ drum rears ,big rear tires and no proportioning at all, AND I upsized my rear wheel cylinders.
Point is, with the big and littles I run; 235/60-14s, and 295/50-15s, The car stops excellent, in any situation.
I had trouble with the factory dual-diaphragm when I installed a 292/292/.508 cam. I swapped to a newer Single unit off a 73 Swinger. Problem solved.

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Hey AJ! What's up man, been a while...
I realize now that my previous post said I ordered the brake line kit with a prop valve, but it's actually just the distribution block. I feel okay with that set up. My tires dont have the size difference yours do though... 245 front, 255 rear.
I was wondering though, roughly what the largest cam I could run and still pull enough vacuum for the dual diaphragm booster? I'm not building a big horsepower motor, I was thinking the cam would be somewhere between .475 - .495 lift. I really want the booster to function properly.