First while the heaters are different, I see a very slight difference in the core inlet/outlets. It would not seem to be enough to matter?
Early heater back side. It may involve a little roto-file work if they won’t move enough by hand.
https://www.flickr.com/photos/advance-design_parts_co/46033227702/in/album-72157631868452754/
1953-55 version.
https://www.flickr.com/photos/advance-design_parts_co/50865146521/in/album-72157631868452754/