Okay, likely a naive statement: black locust is an immensely hot-burning firewood. I would think that if it burns that hot (which would suggest its a dense, strong wood) and if it makes for a good fencepost (which would suggest its a dense, strong wood), then it ought to make a sound neck.
I asked my father about the wood, because he used to make jewelry and other artwork out of all sorts of wood, and he said he loved black locust because it often had borer holes in it that made for neat aesthetics. That's not what you want, I know, so that may be a downside.
As in all matters: Ask Tim. But I also sense that you like to try, to experiment, to dabble, so my money says you'll go for it...
