If you want to insert that into the block, I would be concerned that those threads are not going to hold, actually, the block, made out of spruce, will tear out. I think it is better to go through the block, as Matthew does it, and either bring a washer and nut from the inside, or use a cross dowel, like these, that are strong enough to hold futons together: http://www.rockler.com/product.cfm?page=367
If you bring the cross dowel in from the inside of the bass, I would probably just make a little "keeper" for it, so that it does not need to be repositioned every time you take the neck off: A woodblock, 80% the crossdowel's diameter, with two pre-drilled screw holes, and short gyprock screws half through, can easily be dropped through the f hole. A loong screwdriver is all you need, once you got it positioned onto the bolt coming from through the neck and block.
So many ways to skin this cat.
