How does this heater box retainer rod (J-hook) work?

I know I woke this thread up, but I am going through the J hook part of my resto. Its funny, when I was younger I would be in a hurry and just run the car without it, but being older, and more patient, it would bother me to run the car with that air sneaking in through the gap that is created by not using the J hook. The heater box doesnt seal, and I spent the $$ on the new seals ya know. I just want to do the car right to get an idea of how it must have been when new LOL!