The spring-like strap that connects the choke plates should hold them in (nearly) the same position. Investigate that.
Bench sync is a starting point, if you had the carbs off; you still have to set the sync with the engine running. Carbs mounted, you can lift the CV cylinders through the intakes, using a non-marring tool, like a Popsicle stick and shine a light into them, if you don't want to dismount them. It is hard to see the gap in the plates when the throttles are at idle.
The idle setting screws should allow the throttle plates to close when the screws stop touching the stop, then you can turn them in so they just touch the stops, then turn them the same amount, which will get them close to the same. This assumes plenty of slack in the throttle cables. With the engine running, set the idle rpm by adjusting those screws the same amount, and feel the exhaust pulses from each cylinder. When they feel the same, you have as good an idle sync as they got when your bike was made. Reduce the slack in the throttle cables, then do the same feel test with the throttle grip held open to about 3k rpm, and adjust the cable at one carb. If you want a better sync, vacuum adapters or a Uni-Syn is required.
If you had the tank off, make sure the throttle cables are in the cable splitter fully, so one carb isn't pulled more than the other, or you won't get the throttle sync right.
