What is enough vacuum for power brakes?

Kendog 170 said

1974 DODGE DART 5.9L 360cid V8 Master Cylinder | RockAuto
More Information for RAYBESTOS MC36412
I've had good luck with this. Not sure about the pushrod if yours fits.

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I checked out the ad and the part/[pic you posted is what I had on the car and the local performance parts store sold me the Raybestos MC36439 style. I wonder if they sold me the wrong Master Cylinder?