I just had my heater core done this summer on my 52 and they recored it with modern core and used the top and bottom of the old one they looked for a long time to see if there was a core that would fit but there is nothing "new" so I ended up getting it recored if the shop does a good job it will be just as good as a new one ,it's not cheap but there is not much you can do about it.
Pete
