I agree with txstamp; 6R4 must be correct - besides being a Celler plating, the stamp in question is an excellent match to both of Doporto's examples.
I relied heavily on the Neinken map, but after looking at the Doporto examples who has taken his images from a 6-10 R4 strip of Nathan Shmalo, and a 4-6R4 strip of Tyler Moody, I am left wondering if there is something wrong with the Neinken map.
Neinken's location of the guide dot is a little low and a little too far right of ornament Z1, and he has noted none of the blurs or marks in the bottom margin. Interestingly though, the bottom frame line in the Neinken map looks almost exactly the same as the Doporto examples. Perhaps he just didn't feel the need to note everything, and this example simply underscores the need to look at every resource available.