We are down to 6.
I am leaning toward calling the "Cotton" one - "Cotton" Bogren who was the clubhouse boy for the Cubs at the time (and then went on to be head groundskeeper for many years).
There is a stamp of the Cubs bat boy Gilly Hasbrook - so I don't see why there couldn't be one of the Cubs clubhouse boy (although I wish I had some more evidence).
edit: anybody know the names of the bat boy and clubhouse boy for the White Sox in 1935?? I bet thats who the two White Sox players are. With their sig on the stamp - all we need is name confirmation.