amanico,
thx for your reply and your information. I see what you mean for the crystals, and you must be right since the crystal on the black one is in very good condition: even polished, it's almost perfect, too perfect for a 40 years old watch.
I'll send you the movement numbers as soon as I find time to open the cases.
Interesting pair indeed : sorry that I stole your title ... and good luck for a white 855.
best
karmin