Here's what you' have to do:
2" body lift to clear 3.4
move motor mounts
Use a v6 5sp
change cross member to v6
change rear and front drive shafts to v6
custom crossover pipe for exhaust
figure out wiring
change ps hoses from v6
Use v6 radiator
Thats the major stuff that I can remember
i swapped in a 3.4 in my 1994 4runner and it rocks, but i am also rebuilding a 1987 and i'm leaving in the 22re for the cool factor. it's part of the toughness and authenticity of the truck.
You will never get even close to v6 power with either 4cyl. i been down the road of re-camming...