David, and CRs:
I bought Mavic Mod E rims in approximately September of 1978, when I was a senior at Purdue University. I believe that this was the first year that they were available in the USA. I also bought Michelin Elan 700C x 20 clincher tires at the same time. Clincher tires have been my primary wheelsets ever since that time.
I rode the Hilly Hundred weekend fun ride in October of 1978 on the wheels I built up with those rims. Incidentally, there are great pictures on the ride website of http://www.hillyhundred.org .
I can't reliably comment on the introduction of the Weinmann concave rims. However, the Concave rims are tanks compared to the Mod E. (Note: Mod 3s were the same except in the 27" size).
regards,
Andrew Gillis (Long Beach, CA)