Oops, now that I re-read your post, I can say that you don't need to go real thin, most heavy war bows are around 1.5 inches in the handle, and since you are trying for around 60-70 pounds, I think you can go even thinner. I wouldn't give it a real deep "D" section, more of like a shallow mary-rose bow kind of section, but that's just me. I've had pretty bad fretting on white-wood D section longbows. I think your crowned back will help.