Whoever put the engine in it probably did a short block. If that's the case, it probably has stock heads on it and could even have factory bolts in it still so it would make sense for it to lift the head. If it needs a head gasket just tell him to go ahead and get the KDD O-ringed cylinder heads and make sure it's got ARP Studs going back together.
Honestly sounds like this thing will end up being a money pit just like every 6.4 but if he can get it for a good price everything is fixable with the right parts. If it's for sure got the pistons taken care of that's a big deal for sure but I'd be worried about it even having that at this point.
If he does end up getting it I'd be glad to help with any parts that are needed and whatever advice I can help with, my email and contact info is in my signature.