Thanks! I had seen a couple of those links, but the connection to the National Copper Plate Set is helpful. If I'm reading correctly, the Sporting News supplements were based on the Copper Plates, which means he has a total of two issues. And if that Christie's auction is any indication, I might be able to pick one up for $500-$1000 if it were to ever appear? I'm not likely to find the framed plate plus cut autograph for $116 (!!!) like in that 2006 HA auction.
This seems to clear it up:
http://www.sportscollectorsdigest.co...ate_portraits/