Looks like there's a few radiator restoration shops around. I'll contact a few and see how much (and if) to do a heater core. Either way, i'm not discarding this one. I even kept the original motorcraft Evap I took out after sending a borescope inside and seeing it spotless inside. Considering you can't get them, I think i'll flush it, cap the ends and squirrel it away.
Yeah, it sounds crazy to talk about contacting a resto shop to recore a heater core, but given the discontinuation of many Fox parts in the last few years, I think that's where we are headed over the next decade or so. Rebuild and restore, vs head to the local autozone.