I'm thinking of some heavy duty L brackets bolted to the truck with a 3/4" plywood for a seat with a foam top, a seat back kinda like the seat plans posted above that joker posted...btw thanks for that, with some universal seat belts.

 

Firstgenfanatic, that looks just like the one in my truck.
The bottom cusion is 56"x16" and the back rest is 56"x8".
Here's the link to the pics of mine:
https://www.dieseltruckresource.com/...=club+cab+seat