here's a few I've run across on a quick google:
Those are various years and 12-14 footers, but it's all pretty close to 1979 and the same manufacturer.
Here's the only 14 foot 1979 valco picture I could find:
I'm no expert on Valco's, but I'm going to guess someone has been mucking with your transom in the past and that two piece angle brace is allowing the transom to lever back and forth at the top on bumps while trailering.
I'm willing to bet if you spin those two nuts off and look at the original brace underneath it, the top has been cut off so someone could remove/replace the upper transom board at one time, could fit a certain motor mount of it just corroded away. That someone has been mucking with it is further supported by the volts and nuts that go through the data plates. It would be quite odd for an OEM to build it that way...
Making it worse is the fact that the original brace is probably doing it's intended job properly (bracing the transom) and the upper board it probably "levering" at the top of the bottom bracket (if it's cut off). Coincidentally, that looks to be right where your light gauge bench seats are attached to the upper transom board
and they're broken through...
I could be wrong though, that's a fancy looking patch piece if it is something someone bolted on there after the fact.
Come to think of it, I haven't been able to find any pics of a valco with parallel benches in the back; they're all transverse benches. If someone was good enough to make a fancy cover over the transom brace like I think has been done, two benches would be an easy task. They may not be original either, which could explain why they are pulling off the transom....