I got a free guage type sync tool after a buddy bought it so i could snyc his carbs. he also bought me the snyc tool for adjusting the screw and nut. along with a 90 degree screw driver for the ideal screw on some bikes. told him i would rebuild and bench sync his carbs for free so he told me it was my payment.
I looked at making the liquid filled sync tool using some clear hose and blue water. but it seemed to be a messy alternative. but i never tried.
the guages he bought were great and did not bounce around but the supplied valves are to reduce the gauge flutter. the gauges do have to be tuned before use. basically you adjust the needles to read the same thing without vaccum.
as for the fuel tank i used an old rear end oil bottle with a cutoff valve and filter in the middle. then i hung it with safety wire from the handle bars. you do have to add a vent so i bought a 1/2" replace vent for a fuel can.
carb have all types of different configuration so take the time to look at your carb or carbs and be familier before you being work. if you are not going to take the time to do so than you may be better off not messing with anything!
as far a which carb is the master, the master carb is the one which every carb "keys" to. so look at your carb and see how they are connected. most of the time this carb does not have a butterfly adjustment, other than a idle adjustment or slide adjustment.
and fuel can feed anywhere lost of multi carb units have cross feeds. and someone said something about why the carbs are not made togther or something, I think, well the reason is because the same design can fit many different bikes and may fit anywhere from a one carb set up to a four carb set up.
PS check this.
http://www.xs400.com/forum/showthread.php?t=6050