Use a vacuum reservoir with a one way check valve and you can get away with a pretty lumpy cam. I like to use a small refrigerant gas cylinder as a vacuum tank if there's enough room to mount it out of sight under the cab or bed, etc. A tank that size will allow 2-3 brake applications even after the engine stalls before power boost is lost.
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!