I am a lucky guy. I too was seeking a heater core for my deluxe fresh air heater. I spent I dont know how many hours on the internet looking for the real deal, looking for cores with similar dimensions and connections. All with no result other than a twitchy eyelid. I finally decided to take my core to a radiator shop and see if it was ok. I check the yellow pages, and found just one radiator shop advertising there.
I pulled up to the radiator shop, which looked like it hadnt been busy in a long time. As I crossed the threshold, a deep voice rang out of the back of the back of the shop. "I dont work on those anymore" says the white haired, overalls wearing owner. The conversation wasnt going anywhere fast, the gent saying that he was more or less retired and he explained how my heater core in my hand was a honeycomb design and nobody in world uses that anymore, its not available and its too hard to work on.
Then, out of nowhere, the old gent says......"I got a new one though" I said "No kidding, lets have a look" The old gent digs around in a metal storage cabinet and pulls two new heater cores out. As he continues to talk, it turns out that this man had made up a batch of a hundred of these cores many years back. These were the two remaining examples. After some back and forth conversation, the gent agreed to sell me one of the cores, my choice for a hundred bucks and yes, he would trust my personal check.
I have installed my prize in my heater. I have to hook up the heater hoses yet to try it out, but it was a pretty close fit, a couple of the screw holes needed a bit of coaxing. I got my heater out of one of dad's junk trucks, and I have spent many an hour grinding and sanding the waste products of rodents out of the guts of the heater. After all that work, a new core and blower motor and a coat of paint, I am a proud papa.
One of the last treasures we have in this country that will be sorely missed, is those old white haired overall wearing men who kept our wheels rolling in the years before everything had a wire sticking out of it. Fella's, we will miss you.