Larry,
I'm pretty sure that marks for reproof existed prior to 1960, and, I know the Nazis had a series of proofmarks that were applied at both French proofhouses during the war, but, as to what they were for sure, I don't know.
Reproof has been going on in Europe since just shortly after proof was started, and I know I have seen French guns that have an R on the barrel flats, that I would bet had been put there well before 1960.
I am pretty confident the proofhouse would put more than just the new chamber length, on a gun submitted for reproof, in any European country that has a proofhouse.
Best,
Ted
