Photo taken from Biennial Report of the State Highway Commissioner - 1916
View this photo at books.google.com
BH Photo #509315
Filling in a few gaps:
The original route for this road would have been M-10, from when the state trunkline system was implemented in 1919, up through when the U.S. highway system was implemented in 1926.
From 1926 to 1932, this route served U.S. 23. At the present-day junction of 23 and M-65, 23 would turn north and run up to where the junction of M-55 and M-65 is today, before then turning east along what is now 55, and going into Tawas City.
1932 was when the current shoreline route for U.S. 23 was completed in this area, at which time it was re-routed onto that and M-65 was extended south of the current 55/65 junction.
The NBI gives 1951 as a build year for when the bridge that's currently at this location was built. Assuming that's when this girder was replaced, M-65 would have been the trunkline on this route then.