How do I pressurize the intake manifold?
 

I want to check for vacuum leaks. Clarks-garage says to pressurize the manifold but there is no procedure. Just disconnect a vacuum hose and hook that up to a compressor?

Arnnworx makes a good specifically meant for this. A home made one can be done with an old fuel filter with some air fittings clamped into the jboot. It's not a perfect fit but works. You can wrap some duct tape around it to make up the difference. Don't go higher than 15-20psi

Not possible to pressurize the intake manifold with camshaft installed. . .is it?

I think there is a point where intake valves are closed and exhaust valves are open.

It's a 4 cylinder, 4 stroke engine. There should be no time when all the intake valves are perfectly shut.

The one that will be open will obviously not have the exhaust open at the same time however, so you will be pressurizing that cylinder as well as the rest of the system. As long as you have compression this isn't an issue. The cylinder should easily hold pressure at 15-20 psi. If not, you have bigger issues.

I'd think at least one cylinder would always be on overlap.