Whitch engine size?
The 3.8 are awsome motors for longevity.
What year is the van?
The motor you have should last you 300,000 with good care
I have seen many with as many as 500,000 and still running.
I have the same motor in my 93 imperial with 196,000 still runs like a top!
The motor is very good. But do know that with 176,000 there may be other things that atach to the motor that may go out sensors, ect. Just as with any car with any milage.
I wouldnt be worried about the purchase but just remember anything can happen!
Good luck with your purchase!