What brand hitch is this?

Many older hitches didn't bolt to the trucks frame rails. My 1st hitch was a 12k Atwood sliding bar jaws that was bolted to the wheel wells and framing under the bed. Remove two pins over the wheel wells and the whole hitch came out.
They were what they were for that time and era.

I would get dad a modern 4 way pivot hitch. Those old hitches didn't articulate side to side were bad about getting a pin hung in opening ....especially when the ground has the truck/trailer in a twist. I carried a pinch bar and crow bars as we camped in lots of primitive camp areas. A hung pin is frustrating the first time it happens.
A 4 way pivot hitch eliminates the problem.

Bed rails should be bolted to brackets that are welded to frame

What I'm wondering about is how the rails are intended to bolt to the truck. They are farther apart than the frame rails. But if I unbolt the vertical brackets and flip them around they might possibly line up...

My dad only needs this hitch for occasional towing of a lightweight 19 ft trailer.

Looks like a OLD RWB sliding bar type hitch
Rotate the spring loaded pins and you release the hitch from the bed brackets.
Hitch slides in/out under the raised lip of brackets

They make an OK Boat anchor......

Time to upgrade to 4 way articulating hitch head

The pictures are not showing up for me. Here are the direct links:
https://lensdump.com/i/j4fzrQ
https://lensdump.com/i/j4fS3a
https://lensdump.com/i/j4feNe