Rick,
As to whether the St. Philomena truss came from US 50....it's possible, albeit I'm not seeing any documented connection as it dates from 1904, while the old covered bridge on 50 washed out in 1888, meaning an iron bridge would likely date from 1888-89. Of course, it's entirely possible that a bridge was rebuilt in 1888 and then replaced again in 1904 by the bridge that was later moved to St. Philomena.
I'm planning to do more Clement County research this evening when I have more time; maybe I'll come up with something. Also I want to dig into some more of the covered bridges on the county historical society page!
Paul,
I've never put very much stock in this notion as it was just rumor, I do not even remember the source. Plus, I've always thought St. Philomena looked a bit smallish for the 50 site, although it isn't a huge crossing.
Basically, it was your theory that made the rumor seem plausible---and who knows? Not out of the realm that a replacement bridge in the 1880's didn't make it very far.