AoA noman bhai,
Which model of Mini Pajero does your friend has? prior to 98 models have three speed forward auto i.e. top gear available is 3rd, 98 plus models have four speed forward auto. Therefore, these newer one's are less fuel thirsty and feel more powerfull.
Regarding the question of going for a swap, yes it is possible with Junior Pajero engine, but its 1100cc not 1300cc, junior's engine can be fitted on the same mounts, but you have to change the differentials as well.
I myself have a mini pajero 660 cc auto 2001 model.