Obviously we have no film of Blackburn, and plenty of Louis. However, contemporaries are known to compare fighters’ styles. What were their similarities and differences?
Nobody alive has seen Blackburn box. Based on testimony, we'd say not at all. He was quick and loose-limbed and seems to have held most of his power in his left rather than his right. A thing they did have in common was a (reportedly) good jab, a killing jab, but Louis got his jab at least in part from Williams not Blackburn. All in all, they sound pretty different, as you'd expect from a welterweight/heavyweight.
Hard to grasp Blackburn's style, as most of his fights were held in PA and PA newspapers weren't very good at describing the styles of boxers, too much boxing going on almost every day, so they cut bout descriptions to a minimum. Jabbing a lot, if the opponent tries to close, uses the right as well, at in-fighting short punches to the head with occasional punches to the stomach. Good mover, good blocker, not a hard puncher.
And Gans was apparently heavily influenced by Fitzsimmons, I’ve read that he called the Fitzsimmons of Jeffries 2 as the best fighter he ever saw. Although, I don’t have a source. I’ve seen a few comparisons of Gans and Blackburn, and of Fitzsimmons and Louis from time to time as well. Perhaps there’s a small lineage: Fitzsimmons, who heavily influenced Gans, who heavily influenced Blackburn, who heavily influenced Louis.
Do we know what Blackburn did teach Louis? Did any contemporaries compare their footwork, foot placement, punching techniques?