Engine swap is quite common in Pakistan, due to the fact that sometime overhauling engine costs more then purchasing a kabli engine.
But, incase of Vitz there is a problem, Vitz is a full electronic car which runs through computer, if every thing goes fine, then you will love the drive of 1.3 engine and you will never sell this car.
But first search this forum for vitz problems, kafi sary logo ko vitz CNG py sahee ni chal ri , even wo wali b sahee ni chal ri jinmy CVT transmission ni lagi howi. Kafi logo ko yeh samjh ni aa ri hy ky unky breaks kyo sahee ni lagty (altough their cars have ABS).
Mery ik friend ki vitz ka engine sieze ho gya tha karachi my, he talked to mechanic about swap and mechnic advised him not to swap, instead overall the engine, he used genuine parts and cost was around 25K +OIL+PETROL. His 1.0 liter car is now working fine since two years and he is quite happy that he did not swapped the engine.
SO, find a good mechanic, and overhaul your engine, engine replace kerna ik risky kaam hy aur agar engine sahee install ni howa to ap ko car sell kerna mushkil ho jayee gi. Generally 50K kaam milty hy agar engine swap ho. Agar yeh afford ker sakty hy to phir koi problem ni hona chiya risk leeny my.
No pain, no gain