Yes the through truss is one of the original trusses. The other truss was destroyed by a flood in either 1927 or the early 1930s and was replaced by the pony trusses.
According to my research this is not the first truss bridge at this location. Attached is an image from the 1898 Frisco Headlight Flashes brochure on Van Buren, showing the water plant and the bridge at that time. The water plant, while now gone was adjacent to the first and second bridges. It is possible that one Pratt span was washed out, and replaced with the two pony spans, and the remaining Pratt span is 1898, which, if so, would make it one of about 4 pre-1900 bridges still extant in arkansas.