Against what is written in the head of the dat files (the file informational part), there exiast obviously cross mixes of 737 and 3176 parts, but those odd combinations seem to be quite rare. Among nearly 30 couplings with 737 plate I have none with the hook with year 1966 shape.
Same with 3176 plates and hooks in 1967 design.

go to

http://f24.parsimony.net/forum61776/messages/90682.htm

for more about that story.

Ben