petrol engine, 6g72 costs around 150,000 rupees in shuba, peshawar. cheapest alternative is a rebore of your 4D56 but personally i prefer changing engines, rather than boring them out again. a 4D56 engine minus the tranny will cost around 50 thousand. trade in ur seized engine for around 10 or so.
regarding performance, please explain. performance is a relative term. when compared to the 6G74, the performance of the 6G72 isnt good. compared to the 4D56, the performance of the 6G72 is good! it wont be phenomenal though. i mean, ur regular corollas and civics are still quicker than a petrol pajero.
if u use ur pajero for regular daily driving and a bit of offroading, stick to the diesel. its much cheaper.