Paul, I'm only as good as the information available. This might be a futile search. But search I will...
Clark,
That was my assumption too. My point was that of the two Miami River spans in Pleasant Township, the OH-47 bridge was built as a steel stringer in 1952 and the CR 21 bridge is a Whipple truss, hence neither of these can be the bridge pictured in the 1963 flood photo. I am 80% certain that that the correct location is OH-235, given its close proximity to Pleasant Township and given that the bridge appears to be a highway span of possibly 1930's-1940's vintage, however it might take the expertise of someone like Melissa to confirm this.
The bridge in this location shows a 1986 build date. Perhaps the 1963 in the photo caption is the date of the flooding shown.
This one has me somewhat puzzled as the photo caption in the link states "1963, Pleasant Township", yet the only two Great Miami River crossings in Pleasant Township date from 1882 and 1952, respectively. As the photo appears to show a heavy duty, likely highway bridge, I suspect that the photo may actually depict the OH-235 bridge on the west edge of De Graff, which is within 1/3 of a mile of being in Pleasant Township and is shown in historic aerials to have had a polygonal through truss up until 1986.
Melissa,
From what I've seen your track record is very good. I'm sure that if there's any information to be found, you will find it!