I'm afraid my memory is a little bit hazy on how exactly I arranged the angle plate and vice, it's been over 40 years since I last used then. They got put away when I acquired other tooling. The lathe still gets used on the odd occasion just to make sure it still works, but just for very simple turning jobs now.
I think that I bolted the angle plate directly to the cross slide tee slot and then the vice to the angle plate. This would have given very limited and not very accurate vertical adjustment. I cannot remember if I managed to arrange any fine vertical adjustment, if I did it was probably some lash up using the compound slide as I had nothing else in those days.
The block (B) is still a bit of a puzzle to me, I can only speculate on its use now that you say there could be a locating detent in the face.
I'm sorry not to be more helpful, I just wish that I could remember more clearly just how I did.
Neil