Scott
I never feel good about my id's.
I remembered Agate Type did an article/blog about Topeka Jack and a Union Giants photo awhile back so I went back to find it.
After comparing the two photos they had plus seamheads database shows another headshot of what they identify as Johnson, I came to conclusion in my mind that it was him.
Is it 100% definitely him? I wish I can say for certain but I can't but if this is really the 1907 team, there's a really good chance that it is him.
By the way, the guy with the mustache is George Hopkins.
Steve