Buying older Disco for Son, What should I watch?

[Sonofsam]

I owned a 99 Disco I, a 2003 Disco II, and a 57 SI. So I am not entirely new to the LR scene. Its time to get a car for my 16yo son (oh my god) and he wants a 4x4 versus a car. I want something that is relativly safe. Unimog, HMV is out so the only logical conclusion is a Disco. Odly he doesnt like the old RR's. In my price range I am seeing 95-2000 models with 90-190k on the OD. Obviosly looking for the lowest mileage possible but for one in good condition I would compramise. I am seeing alot of 4.0's with what owners are saying is a head gasket issue. I am wondering if this is a common problem in the 4.0. Is there an easy way (short of removal and dye) to tell if its a cracked head or block vs a gasket. I am comfortable removing the heads, decking and replacing. But a good deal could go really bad if I have to buy a $1700 head. Any input is much appreciated. Or any for sale either in NJ or NC is also appreciated.
Thanks
Son of Sam