Is the blockwork already built up on the rake? If not you can nail it beforehand. Otherwise tosh one through top and bottom, not ideal. I've never really thought about nail position just do what looks right. A nail wants to be 2/3 into the back 1/3 into the front usually so just work on that principle. Obviously you dont want it near the thin cut edge it won't be doing anything. You want quite a lot of meat.