The heater control valve was seized, to the point where the dash temperature cable had broken from trying to force the seized valve. We sent the valve to Jim Tucker (heatercontrolvalve.com) for resto.

We set about rebuilding the 70 AC/htr box. Removed the heater core, along with the bypass valve and checked for leaks. Did a pressure test and it leaked from the core, so we ordered a commonly advertised aftermarket unit. It was a nice piece and physically fit, however the tubes did not line up properly with the bypass valve and the copper fitting to the firewall.

We returned the aftermarket unit and shipped the OE core/bypass to Glen-ray. They discovered the bypass valve was also leaking. This presented a problem because they indicated there was really no one around rebuilding the bypass valves. They did supply a contact but he said he stopped rebuilding them several years back. After a few weeks of interweb research, located an A/C company in Texas who was selling what looked to be an identical, new bypass valve. After comparing dimensions with them, I had it shipped directly to Glen-ray so they could test the whole unit. They said it was identical to the OE piece (and asked for the source so they could use them in the future).

When the core arrived, we began the box rebuild using one of the resto kits which supplies weatherstrip and such. The evaporator section was cleaned and pressure tested. The evaporator drain tray was a bit eroded from the years so that was cleaned and coated with POR15.