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

most of our old cars have been "worked" on thru the decades on one waay or another, to find a 50 yr old car that has "survived" getting hacked, screwed up, mutilated, violated, and just plain F---- up is rare! all this reminds me of the "low mile" speedo that is correct BS I read all the time!? ha