I used to use a complecated device like this one for my BMW r80rt....haven't used it on my GL yet as it's to cold out and the bike is not running..
It is just a section of 1/4 pvc tubing approx 16 ft long ,doubled around and filled with chainsaw bar oil, add a bit of varsol if it is too slow to react.
when the fluid evens out(or very close)while the bike is running at idle and above 2500-3000 RPM.then I would consider the carbs fairly well synced.
For the adapter screws ,local Honda dealer or aftermarket shop..........or make your own.
I made one like this and it works very well -- no need for the fittings on the lines if you're syncing a twin. (of course you need still need the fittings on the intakes)
To reduce the pulsing, you can add an inline obstruction by putting a one-inch piece of the next size smaller tubing in each line. (tip: with vinyl tubing, the ID of a given size tubing is the same as the OD of the next smallest size)