read about this in Peter Alexander's book,
The Gunsmith of Grenville County, and made my own when I had a small drill press. Then, when i graduated (i.e. splurged) and got a full sized drill press, I kept it and put it in a hardwood clamp so that I could use it in a cross vise (that is, one of those cool threaded vises which will move along the x and y axis, then you lock it down and it's there forever.
I agree that having a longer threaded portion is more useful. If it gets in the way, back the locknuts off and lower it down.
By way of 'learned it the hard way,' you still must take care that the line of the tang bolt is perpendicular to the curve of the stock, otherwise the bolt head won't fit properly into the tang, and you'll have to do a lot of embarrassing filing and fitting.