for any machine there are specific test procedures outlined by the manufacturer to determine if repairs are required.
In your engine case, you first need to have its health checked, a compression and oil pressure test can tell you quite a lot, a leak down test can tell you even further. All these can be done by a good smart workshop - not ustaad G. (Ustaad G is stuck in pre 1947 ways of working)
secondly the bhoon bhoon noise you mention is a classic symptom of worn engine mounts (fondashunn in ustaad G language) of if you have automatic gearbox,the torque converter is buzzing or the trans itself is making noise.
regarding swapping out a scrapyard/junkyard engine - I never advise for it unless you are going to test it thoroughly first before shoving it in the car. - Check your old engine first, 90% of the times its good for service.
