Not quite - the plumb-bob will always point through the center of gravity, regardless of the plane's orientation. That is why it doesn't really matter how you suspend the model. But by suspending it from the nose/tail, you can also check lateral balance as well as fore/aft CG.

As for a plumb-bob, I just bent a small loop in the end of a piece of music wire about 8" long. When suspended with thread from the suspension point, I find it very accurate. Certainly faster, cheaper, and easier than any other means IMO.