If it were me, I would not cheap out and go new. What if the used is failing or on its way out, a few thousand miles later?

2017+ Pacifica Engine Failure Owner's List | 2017+ Chrysler Pacifica Minivan Forums

With used you are rolling dice. New you will have a warranty.

 

Why not just get 2 brand new heads. Unless the bottom is locked up why the whole engine?

 

Because if it's what we've seen previously the cylinders themselves have been worn biggly and heads won't fix it. They've tried it on other engines and it's basically back to drinking coolant within 10k miles and it cost almost aa much to put heads on as it does to swap the motor because of the labor.