What to replace with the engine out?

So I'm replacing the engine in my 2000 DHSE (172k miles) after an overheating/ blown radiator issue that has probably cracked/broken something deep inside (as its running like a bag of scanners and belching out black smoke).

So my question is this with the engine out what is worth replacing that can't easily be one any other time.

Apart from obvious service parts and fluids I was going to put in a new thermostat and fan belt but is there anything else I'm missing?

Cheers

Gearbox if it's an auto, water pump and all the hoses.

Are you suggesting putting a new gear box in or just a oil and filter service? I'd rather wait till it goes as after forking out for engine and labour to fit it I'm a little broke.

I've got a couple of spare oil pipes (ones that run to and from the oil cooler) that I was going to stick on.

I'll see how much a water pump and hoses are and order them

Thanks