I recently bought a 2001 XJ that now has 210,xxx miles....and I drive it daily 40 miles round trip for work.
Check under the oil fill cap for evidence of coolant intrusion. Be sure to check the fluids for condition. If everything checks out buy it...The head cracking itself is not that big of a deal as a new one can be had for ~$400. The issue is if the coolant stays in the oil pan for too long, it leads to crank bearing wear which is more timely and expensive to repair.
But not all 0331 heads crack. so check it out and looks good, buy it.
2009 WK Laredo QTII
Formerly: 2001 XJ, 200k+ miles.