Naw, won't spill--if the vacuum petcock is working properly, you can just disconnect the fuel line from the carbs and pull the tank. I've not had any problems with doing this. Note: If the petcock is in the Prime position, it's a wide open valve and would spill fuel everywhere if you disconnected the hose.
But I've not heard of anyone having a vacuum petcock problem and didn't' already know it--so you should be fine to pull the tank.
BTW, the yahoo group files include a maintenance manual; I bought one from Kawasaki--either way, an indispensable reference for those like me who don't have a mechanical background . . . . .