just use the guages for syncing,taking them off for a pre vacuum "bench sync" is a step backwards as your only making work for yourself,be sure the ignition is set perfectly,use a strobe to check the 1/4-2/3 timing,if they are slightly out with each other the vacuum sync will be hard to do and any bench sync wont be worth a damn,,adjust the main idle screw untill its threads just come away from the lever it pushes then wind it back in a turn or two,,then with the sync adjusting screws wind them one by one letting the throttles drop slowly untill they stop,once each one is down turn those screws one turn to lift them again a little and restart your vacuum syncing,,youll have to fiddle with the throttle to keep it running and the idle screw will need tinkering with.