Metering rod gauges are no longer available, this is the procedure now recommended:
Back out throttle lever set screw to allow throttle valves to seat in bores of carburetor and loosen metering rod arm clamp screw. With metering rods in place, press down on vacumeter link until metering rods bottom in carburetor body casting. Holding rods in downward position and throttle valves seated, revolve metering rod arm until finger on arm contacts lip of vacumeter link. Hold in place and carefully tighten clamp screw.