Dave - You can use one gauge but you need to follow the sequencing, #2 is the non-adjustable one, so #1 and #3 work from 2, so you need to get #1 and #3 right then #4 and you may end up going back and forth a bit with just one gauge.
Some guys do it using tubes off all four carbs and a bunch of aquarium aeration valves to turn on/off various carbs instead of having to change attachment.
But in addition to your gauge, you need the adapters to put in the threaded hole where the plug was, to which you attach the flexible tubing. Be really careful because the threaded tube adapters are very small and easily broken off. I attach the flex hoses to the adapter, leaving the other end of the flex hose free until the adapter is threaded in, then I attach the free end of the flex to the gauges. But I have a four gauge bank. If you look online, you can get a 4 gauge set with adapters and carb sync tool for about 85 bucks plus shipping.
Or if you want to really cheap out, check Youtube for examples of just using flexible clear tubing. But if you do that use motor oil in the tubes so anything that accidentally gets into your motor isn't going to do harm.
Also remember, you need to have your compression within reasonable bounds across the board and your valves and timing should be set right, otherwise don't even bother with vacuum sync. And your carbs should be in good shape and bench sync'd. That gives you a solid starting point. The vacuum sync is meant to allow for minute changes in valve lash and ignition, but those things need to be as close to spot on as you can get them first.
And back to the temp tank thing for a sec, whatever you use, put a filter on the thing. It's too easy with temporary things and fueling up from a Jerry can to get some debris in the fuel.
