engine not producing enough vacuum

Hi everyone
I'm in need of some help.
I bought a car with a 440 6pk setup in it and I've found that the engine isn't making enough vacuum to operate the brake booster or the outboard carbs so I need some suggestions as to what maybe wrong so I can correct it.
I can offer this info to try and help.
Lunati cam number 10230703
Advertised duration is 271 int 279 exhaust
Advertised lift is 494 int 513 exhaust
Lobe separation is 110
Has 1.5 ratio rockers
Engine is producing 10 inches of vacuum now but lunati says it should be at 15 to 16 .
SO WHERE DO I GO TO LOOK AND CHECK NOW?
PLEASE HELP

THANK YA'LL IN ADVANCE