Since this video doesn't show much in the way of setting up the carb sync equipment...
So towards the front of the carbs on the outside/bottom near the intake manifold there is a little plug that blocks a port. If you remove that plug you can thread in the brass nipples that come with the kit. From there you should be able to run some tubing from those nipples up to the 2-way valve at some convenient location, usually near the tach somewhere. from the output of that valve you should connect the little plastic in-line valve, and finally the gauge.
That would be how the setup in the video is configured. the 2-way valve is to switch between each carb, and the inline valve is to throttle the overall airflow back a little to help steady the needle on the gauge so it doesn't jump around so much.