Nationals mandolins used a neck stick. If you look at the picture of my guitar you can see it. It's set into a slot in the neck. This runs the length of the instrument to the end block and is also attached at the soundwell the cone sits in. Additionally there are usually screws through the fingerboard that hold it to the top.
Mandolins use a biscuit style cone.
I'd recommend a National or Quarterman for the best tone. As far as metal, brass will sound best for a mandolin but it is pricey. I hand carved a maple neck and made the sound well out of bendy board. The top is solid spruce and the hardware is all standard dobro that I ordered from Stew-Mac. It sounds great and will actually be played by a friend in concert next month.