From a safety standpoint, front seats can usually hold more load. I say that because they typically weigh more, and have one of the belt attachments to the, vs most anchor points to the floor.
It is was me, I would build a tube structure below the seats and tie it into the truck frame. The Screw rear seats are considered a stadium type seat, and there is nothing in the body to anchor the front of the seats. You biggest challenge will be ensure whatever you design will not pull through the floor. There are usually reinforcement bars or structure under the seats.
The trucks in Chris's photos look like an older body style, which may have had cushion supports before. Those are the long link bars in the front.
To save on size, I would look at second row Flex seats. I believe they bolt straight to the floor, so there would not be much in the way feet or hooks to work around or remove.
I have considered doing this also, but not sure if I will get there.