jsut a simple check is to look at your odo, is ALL number line up 100% then you can there is a high probabilty it is genuine kms. my skyline came here with 60000, and it aint straight, so you know someone fiddled with it!
well if your car realli did that little kms that would explain the head corrosion and radiator corrosion, water sitting in a radiator and engine that is not being driven much (30000 /15 years) is bound to do some damage, thru corrosion, from the radiator coolant losing its anti corrosion properties. (prob never got flushed in its entire life)