I will advise to put a brand new engine in it these days its cheap to put new engine then getting it over hauled... because new engine will last longer and will be maintenance free for longer time then the over hauled one.
If you want to know the sources from new engine then, its royal park, litton road, few shops on davis road as well... in any case feel free to give me a call I will guide you, how to procure one, do keep your cnic with you when you go to buy. My contact is 0320-2594328