1955 topo quad shows Pennsylvania RR crossing here.
My guess is the wood blocks are merely to keep the diagonal eyebars in the right position and to prevent from from banging against each other. Non-structural elements.
Sometimes the cloverleafs mean Pennsylvania Railroad was associated with the bridge. By the way, is this bridge part of a SuperMax prison? Looks like the portal is the only thing you can see thanks to hideous fencing. Its the sort of railing you expect to see on an urban freeway overpass in Detroit, not on a rural rail-trail bridge over a river. Such fencing here is in my opinion completely unacceptable. You can't even see the river, let alone the beautiful historic truss!
When I seen the fence inside the bridge I puked a little. The only reason I see them putting this in is the sub division that is basically in viewing distance of the bridge. Just a note to get to this bridge, park on the west side. near the quarry.