You need to restrict the airflow which will slow the response of the gauges using a damper of some sort.
Shop gauges uaually have short small bore pieces of tube that are inserted in the line between the gauges and the Vac take offs on the Carbs, 1 per line.
Older gauges employed a turn screw system that acted on the line to restrict the flow.
To give you a better idea the hole in the restricting tubes are about 1/16" Dia.
In the pic below the Damper/Restrictor is number 3.
