I swapped a 3.4L 5VZ-FE into my '93 4Runner this past spring. It's pretty straight forward. The crux of the problem is the wiring and the exhaust. For the wires, basically you have to match about 30 wires from the body to 30 wires coming from the motor. Kinda hard to figure out, but it's all there. The exhaust is just pain 'cause it's tight. Any decent exhaust shop can fabricate it up though. I did it on my garage floor and took the pipes to a shop to have them bent.....I would suggest having a shop do it though.

There is a ton of info here on 4x4 wire on how to do it. I was able to get all the info I needed here and it took about 3 or 4 weeks playin around after work and on weekends (although I took about 2 months to plan the swap).

For difficulty level, take this into account...I hadn't turned a wrench (other than basic tune-ups) in about 10 years prior to my swap.....so it's really not that hard. The only specialized tools were a motor hoist and a blowtorch to bend and weld brackets and exhaust pipes.