Normally you need 112/114 lobe ctrs. to have decent vacuum for power brakes, your vacuum could be down to around 10 inches or less, where you need 14 to 16 inches of vacuum for the brakes to work properly. I'm in the same situation with my El Camino and i'm changing the cam out with the present cam i have less than 1/2 petal and i have a vacuum canister for reserve vacuum.
JMO
Zip.