I finally got my heater box back from PRDesignSF (https://prdesignsf.com) and I wanted to share my experience here since it was a good one. My car is a 1969 model year. Its currently going through a full restoration. The heater box had a frozen motor, cracks and breaks in the plastic, a broken cable and lots of rust / dirt... it was in bad shape.
I contacted Brendan Pramono at PRDesignSF about restoring my heater box. I sent him the box and he disassembled it for me. The metal parts were returned to me and I had them blasted and re-plated. The plating shop ended up being disreputable and disappeared on me for a several months (long story). Brendan was a total saint and didn't pressure me while I went through the hell of trying to get my parts back and have them plated somewhere else.
I sent back the re-plated parts and Brendan rebuilt my heater box. Took about a month to complete the work despite all the COVID19 stuff. He pressure tested the core and removed the rust, upgraded my heater valve to a new version (since mine cant be rebuilt), added new foam and grommets throughout, new cables, and addressed the cracks. He also added a new motor but used my old fan blade, which was zinc plated. Total cost including shipping was $1239, minus the plating.
It was expensive but the heater box looks fantastic and I couldn't be happier.