1968 Airbox rebuild question

I removed the suspension, forward and aft, gas tank, exhaust system, and then removed all undercoating with a heat gun and scrapers. Then, using hand tools, sanded 100% of the undercarriage to bare metal. And then I primed, painted, and clear coated it. I did the same to the interior, trunk, and engine bay. Zero rust. I had never done any of this before, but this heater core deal has halted everything. Some pics: