Motorcycle Questions? Ask a Mechanic.
You don't need the vacuum petcock but you will need some kind of fuel valve on your tank. The original petcock has a "prime" position to allow fuel to flow freely without the vacuum operation. Just try to get some fittings or a valve on the tank if it does not have one.
I have heard the Yamaha vmax 700 petcock may fit itf you cannot find anything else. There are two lines on the tank that may have to be routed into one line to the carbs. You should be able to see that by looking at the tank bottom if that is the case with your bike.
Let me know if you need other information.