I'm 100% against overhauling the engines (mainly after wasting 70,000 on overhauling the engine from a dirty dishonest mechanic).
But in case of Mehran, I would recommend overhaul. As I don't expect an imported/Qabli carby engine to be available anywhere.
What will you get most likely will be some engine removed from a Pakistani Mehran, and chances of it going long term are rare.
Just my 2 cents...