The collector who runs this site is a member here, but I didn't find a pre rookie prior to 1971 Kelloggs (there were a few later items that weren't from mainstream sets though):
http://www.footballcardgallery.com/s...rch=joe+greene
I thought of one more thing..... In the current issue of GG, there is an article: The Super Collector - Joe Montana Super Collector Don Nguyen
by Jared Kraus
I no longer have the issue, but I was surprised to learn there are literally thousands of Montana cards - I think most of these were issued after he retired, but I would have never expected the count to be that high. Could someone check if any pre-rookies are mentioned?