Does this belong on the heater box?

[Dan440-6pack]

Not sure where this goes.
Thanks!

[RUNCHARGER]

Yup: It hooks into the sheetmetal air duct on the firewall and supports the fibreglass vent box.

[anlauto]

The push nut DOES NOT belong, but as Sheldon pointed out, it hooks on inside the passenger side vent box. NON AC cars only.

[Cuda Cody]

   Yup, the J Hook for the heater box.

[6Pack70]

Just a little tip that I learned on this forum,  when you're ready to install the heater box,  leave that hook bolted loosely to the heater box.  Put the heater box studs through the openings in the firewall, push up on the box assembly and have a friend reach into the cowl from the outside and hook that little hook over the raised plenum inside there. Then tighten the hooks bolt at the heater box. Dont over tighten.  It will now allow the "D" shaped foam seal to seat nice and tight against the upper cowl.