i kept a spare rad from one of my parts tractors just for this reason. think you may be able to get an early 730 rad to fit in there but may not be able to put the door back on. IF its a show tractor you won't be able to do it. could also change front top hood with an early 7/830 hood. Try Don Livingston.
A GOOD rad shop should be able to recore them. Probably $500+ (my 730 one was quoted at $400 about 5 years ago but copper has gone up I think).