Will a new head blow my engine?

Hey Guys. News here. Love the community I see here. So here's my dilemma;

The engine overheated and I've cracked the head. My mechanic replaced the radiator and the water pump (he didn't find the cracked head until after this, a bit shite but I've moved on).

I called him today to ask if it is wise for me to try to replace the head with a new one. He said he wouldnt advise it becasue the engine has done 300 thousand kilometers and the new head might put too much pressure on the engine and blow the engine. Is this a common result? I'm keen to take on the project as It'll give me the opportunity to learn and also to save spendning 5k on a reconditioned engine (really expensive in Australia). The water pump and radiator are new and I'll replace the timing cover as well if i dive into this.

Of all the combined experience and knowledge here what do you guy think my chances are of the new head taking to the engine? Its a 3L Diesel from 2000.

Thank you!

Utter rubbish!

It may blow more past the piston rings than a newer engine but that is how they are made to do just that.

Perhaps he does not want to do the job?