The radiator shop should be able to repair it, if the core isn't in too bad of shape. If you do need a new cor, check the American Classic link above or one of the other suppliers on the Links page, new cores are available.
I take it that the '58 assembly is the deluxe fresh air heater, they are good units and can be swapped right in. You will need the dash control assemblr to operate it. Servicabilty is about the same.
