Yes, the nail is in the cap with the point sticking into the groove the rope seal fit in. It will be obvious which you have when you get it apart. The rope is like an O ring cut in half with half in the block and half in the cap. It will be mashed flat where it rides against the crank flange and makes its seal.
The rubber type seal looks like a conventional lip type seal that is again, cut in half, with half in the cap and half in the block. The idea of rotating the split joint to not line up with the cap/block mating surface is to reduce the possibility of the seal leaking where the two ends butt.
The rubber type lip seal is probably the better (and newer) design of the two. It's lip functions just like any other conventional
oil seal. It is supposed to reduce rotating friction caused by the rope type.
Don't know how easy it will be to rotate the old seal out and the new seal in the block out while the crank is still in. The cap is a no brainer. Certainly worth a try. Good luck!
Dave