Ka24e out of a navara would be your easiest 4cyl petrol power up.
I've got a d21 dual cab nav with one in it (330,000k's) and goes heaps better than my mates Z powered king cab which has had an engine rebuild with cam,weber and extractors.
Pathfinder v6 is another option but a bit more involved in changing plus manual versions are hard to come by.
Terrano td27t diesel is yet another and also a very involved transplant.
I also have a terrano with the td27t and it Is definitely my preferred choice although I do still find the navara fun to drive.
Hope this helps.