Check the current book value of your Liberty. There will be virtually no difference in the value if it has a rebuilt or used engine in it. I would likely opt for the used engine as the vehicle is nearing the end of the line. In a couple of years it will have very low resale value.
If you simply love the car and plan to keep it for 5 to 10 more years then the extra money for the rebuilt motor might be worth it. If you sell or trade it in the next 2 or 3 years the used motor is the way to go.