The max gap you are showing looks fine - should produce a crazy high idling (redline!?) speed, so no worries there. You don't need any sort of guitar string or drill bit. Simply back the idle stop screw out far enough that the throttle plate on the carb that has the cable attached to it is fully closed. Then adjust the sync screw - that's the one you have backed all the way out and the jam nut loose on - so that the "slave" carb has its throttle all the way closed. Operate the throttle grip and make sure that both butterflies just close at exactly the same time - adjust the sync screw until they do. Then tighten the jam nut and re-check. Then start the bike and screw in the idle stop screw until it idles. Remember there is a pilot circuit that will need to have its metering screw adjusted as well - might be a fuel screw instead of an air screw like your RD. If it is on the engine side it is fuel, and you screw it in to lean out the mix instead of out like your RD. That's all you can do until you sync them while running with manometers if you deem it necessary. Bench syncing them as just described will be fine until you get everything else sorted regardless. Doesn't look like you have had them apart. You should know by now that anything less than 100% disassembly is likely a waste of time. You have to remove the butterflies and shaft to change the seals which is usually the worst problem on these type of carbs. Remember, these things are essentially the same as your RD carbs except for the vacuum slides.
