Was looking up some history for a project of mine of Michigan's offensive systems through the years and found this- https://play.google.com/store/books/details?id=le3KCYXt5BwC&rdid=book-le3KCYXt5BwC&rdot=1
A free copy of the 1905 book written by Fielding Yost himself. Yost was 43-0-1 as a head coach at Michigan at the time, coming off of 4 consecutive national championships.
It really is a cool book about the history of football and how it was played back then.
Your linebackers on defense were your left and right halfbacks with the fullback as what we know as the MIKE.
This was written before the invent of the forward pass. The QB was the only player in the defensive backfield. 25 yards behind the fullback!
This is the "regular defense form"-