If using an msd ignition distributor and coil are you eliminating the vacuum connection ? If so would there still be a port on the intake manifold to connect a vacuum guage for setting mixture?

I had to add a port to my phenolic carb spacer on my first engine as the intake or carb didn't have a port.

Marine distributors don't have vacuum connections. They don't need them, no such thjng as light load cruise in a boat.

Correct. Plus, I never suggest nor promote driving a boat down a steep hill.

where do i hook up the vacuum
gauge to set mixture?

Are you set on doing your idle mixture setting by vacuum?? You can do it very easily by turning mixture screws in a little at a time until it drops RPM then turn it out about an 1/8 to 1/4. You can use a hand held tack to help.

Most marine carbs (at least all the ones i've seen) have a vacum fitting. On the holleys it is hidden under the primary float bowl. Hp500 carb came from Merc with one. Has a rubber cap on it.

trhanks, my carb has the port but the holley video shows a port on the intake manifold, will the readings be the same? hand held tach that would be easy because my timing light has a tach read out on it

The port below the bowl is manifold vacuum.