Tommy, call 1-877-542-8192 they will fix you up. There was someone on here with a 61 Ford looking for a heater core that I sent there. He was pretty satisfied. Gary
I ran into the same problem on a '61 Electra. My local radiator shop could order a core that would work much like recoring a radiator. I ended up looking through the catalogs and found one about the same size with about the same nipples then modified the heater box to hold it and modified the firewall for the nipples to come out of. More work at first but now it uses a run of the mill heater core.
I do have a really good radiator shop here in Indy that I can check with also. Looking on Evil-bay I see a couple that are used and leaking for $200.00. Sheesh!
Tommy, Before I'd go with completely redesigning the system, I'd go with a Vintage Air Gen lV Sure Fit Heat & Air Unit. When you deal with Nipples I've always found it to be way more expensive in the long run. What ever you do, don't buy anything Made In China by small children unless you want to do the same job over again real soon. Call that phone # I gave you. Gary