Any vehicle without coolant/fluid in the header tank and radiator is a walk away unless you are willing to spend on fixing any problems that may have occurred due to overheating and fix them immediately before using it, if it was just the radiator cracked the OP would have had it fixed because the cost of a new radiator is cheaper and easier than trying to convince a potential buyer its just a small coolant problem.
it is not good if this engine has been run with zero coolant because you have no Idea if it has been cooked or not and how many times just to get the PO home or off a beach/trail.
You seem happy to have the work done though, I don't have smog tests where I come from but if you are required to have a smog certificate before sale and you have not got one then there is a reason it hasn't got one and it could go beyond the coolant/head gasket/head problem.
Does your mechanic believe it will pass smog once you have fixed the radiator and head? I am sure they would have checked for water in the oil or oil in the radiator already because that's the first thing they would have looked at before doing any other tests.
Just my opinion
