I wondered about the clutch too....because if it hasn't been changed you will have to do it if you drive the car. Can't imagine a 25 year old rubber clutch getting any better with age.
Bit pricey IMO as the SCs are nice cars but there are lots of nice cars in the 15 to 20 K range if you look around a bit. I just had my engine pulled and resealed at 180K miles (for close to the same costs quoted). My head studs and leak down are fine. I would be happier if he had added a set of SSIs and the normal up grades besides the minimum required to keep the car running.
I have an extremely nice '79, but for $18K I would go looking for a 3.2 and a G50 tranny.
All that said I would be tempted to grab it and run
It looks to be a nice car. But I would also want a couple of PP1s. My new rule is 3 of them. Money well spent IMO.