Need heater box & advice - '81 K10 p/u w 350 & a/c

[6772fan]

I always said that GM must set the heater core in the floor and build the truck around it. Anyway, I always remove the passenger side inner fender and you can then easily ensure you've got everything loose from the engine side. In terms of repairing what you have, it can be done, but I don't know that I would trust the repair over the long haul. Check the parts section or Craigslist for a local complete AC heater box replacement. I don't recall which years interchange, someone who does will chime it. Good luck.