The stock seat in my ‘52, when slid back all the way almost touches the back of the cab. I can’t see how it’s possible to mount it 5” further back.
I’m going to have my seat reupholstered and I understand that they can wire some of the springs so they don’t stick out as far to gain an inch or so.
Others have gained room by changing the seat out for a more modern seat. Some have built it seat belts and some are powered.