Master Cylinder Choice

[Smoker03]

I have Wilwood front and rear 12.1" brakes with four piston calipers on a 67 camaro. RIght now the car has power brakes and the pedal is sensative sometimes and very stiff other times. The motor doesnt make much vacuum at idle, and that seems to be the issue. I would go hydroboost, but its not in the budget. I have heard many people say that a manual setup can be just as good with the right master cylinder. Would anyone be able to recommend a master cylinder to convert to manual brakes that would work well with my brake setup? Any info would be great, and I am always willing to purchase from a supporting vendor.