The 3.0 isn't nearly as reliable as a 3.4 so make sure it's priced accordingly. They will go forever but they'll be running on 3.5 cylinder's worth of compression and guzzling gas like a V8 if you don't keep up on valves. 158k is likely low enough mileage that a valve hasn't burned yet like they always do, but if you're pulling the heads get a valve job done anyway (and check for leakage with compressed air and naptha before you bolt on after). Have your friend adjust valves and err on the high side of clearances and they'd be good for a while. For a 29 year old rig you won't find many that are more reliable but it's still 29 years old. I'm rehabbing my '90 (and logged on to talk about how I'm modifying it for safety) so they do have a spot in my heart.