Both aspects have their risks.
I recently rebuilt a engine of a toyota Vitz gen 1.
Honestly I wasnt satisfied. Japani rings had their issues, the car was heating everyday. Then changed them with orignal rings from a scrapped car, then the car could take load, but wasnt running the ac.
If you wana sell the car rebuilt is better. The first question people ask is if the engine is changed.
If you want to keep the car better replace the engine. You will get your car back in 2 days.
A car opened in pakistan is very hard to come back to its orignal state in Pakistan. Very few honest and reliable mechanics. Everyone finds ways to make easy money.
You will face this with a replacement engine aswell. If you go and check your self you might get rates of 45k complete engine. Where as a mechanic might quote you 70k.
Even then you might have to trust your mechanic