Chuck over at GunLab.net is making great progress on the AR-180B lower parts and he just put up an article outlining his procedures for building the bolt hold open.
If you are not following him, you should. His sight is a wealth of knowledge and he is always willing to share it with all of his reader.
Once again, we hope to be bringing these parts kits to you as soon as we can. Let me know if you are interested and I will put your name on the list.