Thanks all your help, guys - really appreciate it. I've dug around some more and here's what I've found.
Re tagging -- Andrew might very well be right. But this one here would make two 66 Cubs jerseys similarly tagged erroneously:
http://jun08.hugginsandscott.com/cgi...?itemid=101112
Maybe Kowano switched to the new tagging system after 66?
This Banks jersey from 69 indeed has the tagging Andrew remembers:
http://sports.mearsonlineauctions.co...entoryid=64692
Speaking of Banks, I note that he wore a size 40 jersey and was almost as big as Glenn Beckert (6'1") so it's plausible that Beckert wore a 40 also.
Finally, Beckert's 67 Dexter Press card seems like it might be a photomatch. The pinstripes seem to align the same at the shoulders, neck and with the buttons.
But maybe I'm just looking through rose-colored glasses. Any additional input is much appreciated.