It would appear the head has been changed, or possibly the entire motor. Does the motor have the Kaiser-Frazer tag on the side?
If so, the head was likely changed.
The engine number should be in 3500000 range.
Another way to tell if the engine was changed, does it have a Delco or Autolite distributor/starter/generator? A '53 should have Delco. If it has Autolite, especially an Autolite starter, then the engine was changed.