I have both types. I got a set of the 81 GTV6 wheels as they are made
of a lighter alloy than the later wheels. In the brochures they call
it "Elektron" if I recall. Anyway the earlier wheels are definitely
lighter. About 14 lbs vs the later aluminum ones are closer to 17 lbs.
I've heard that the Elektron wheels are actually magnesium alloy.
I can't say for sure. Also and BTW. the later wheels say campanatura
which some mistake for campagnolo.