Low Vacuum from crate 360

I have a 1998 Mopar Preformance crate 360 installed in my 1969 Barracuda convertible. The engine is an LA block with Magnum heads. It has an Edlebrock Air Gap dual plane manifold and a Comp Cam (20-614-9) with the following measurements: 264/274, .480/.480, .210/.220 @ .050 lift, 112 deg lobe separation. The tappets are roller hydraulic type. The carb is a Holley 750.

My problem is there doesn't seem to be enough vacuum to run the power brake booster. The shop where the car is says the engine is only producing 11.5 inches of vacuum. They're going to check the timing at both Idle and at 2,500 rpm and also tune the carb to see if we can get closer to 16 inches of vacuum.

My question is: could I have a vacuum leak and if so, where would I check first?

Thanks for the help.