This an early version of the model w/ "600" marked dial [instead of "600m"]. It's super clean & it was previously owned by Randall himself! One "deviation" from fully original is the cyclops [on crystal over date display].
This is one of my favorites in my collection!!
One thing I like about the 6159 PRO divers is the movement. It's from the same family [615x] as the Grand Seiko Special watches!! As you may know, a Grand Seiko Special [6155 or 6156] is a "step above" the regular Grand Seiko [6145 or 6146] of the early '70s. The GS Special was constructed to a "AAA" standard while regular GS was to the "AA" standard. See details in my posting about Seiko Accuracy Standards in the main section:
The Patron Saint of Seiko Collectors