USA made ONLY, and if at all possible, NOS Ford.
Re-Coring used to be done years ago, and I have actually done it myself when I owned a radiator shop in the early 80's but in my opinion, not the best way to go. We would saw out a section of heater core stock from a large 'chunk", the size and thickness of the original, melt/clean off the rough edges and then solder on the old tanks. It worked very well, but I'd say it worked well in a pinch since even with all of the equipment of a radiator shop, it was rather a P.I.T.A.
QUALITY really matters in this application especially since the job to go back in to change it later is so huge on these cars. Do not try and buy this part on a budget. I think I saw a NOS one on eBay last week. It fits many years and other vehicles into the 80's, even Pintos with AC if memory serves me correctly.