The old radiator was leaking beyond repair and judging by the image top left the tubes were so 'furred up' and blocked that it would not have been very efficient either. You only need to look at the top view of the new core to see the difference.
The old rad was stripped down to its component parts as shown and these were then shot blasted back to bare metal.
Once cleaned and checked, all of the parts were soldered back together before testing and inspection.
The finished radiator re core can be seen in the final image.