[Turbowned]

It's common practice with Subaru to replace short blocks when there is an issue. Since there is no cylinder head damage reported, there is no need to replace them as well. All the technician has to do is ensure that the mating surfaces are clean, that the gasket seats properly, that the head bolts/studs are torqued down properly and that the timing is set. They probably have a dedicated technician or two to do engine work; that type of thing doesn't just go to the rookie hourly tech.