Ken,
have no idea on late bay, but early bay arms fit the split beam, and I think its 69 bay ones that allow you to have discs, however if you want to go low don't go bay, stick with the split and buy a disc kit. Type 2 detectives sell a Porsche kit that has everything (I have one and its good) or look at Red9 Design as they do a kit also (you can use it with their A arm front kit which uses bay spindles). if your split beam is solid and not rusted out, keep it... Ken.