I just did it not to long ago. Why, you ask? My 98 Taco ext-cab 4cy 5spd 4wd got taken from me(rear-ended and totalled) 2.5 years ago. I was all excited to get a 01-02 4wd double cab but two weeks after the accident, we found out baby #3 was on the way! Double cab dreams smashed but it was all good. We already had the 2000 2wd 4Runner but wanted a slightly bigger family vehicle so the insurance money funded a new to us 06 4wd Honda Pilot. I inherited the 4Runner and daily drove it for a year with my Taco wheels and 265's contemplating what to do. It was definitely not that spunky with the 265's and 3.73 gears.
After tons of research about swaps and also looking at selling the 2wd and buying a 4wd, I settled on doing the swap. Reasons were, I couldn't find suitable 4wd 4Runner to buy. I knew the history on our 4Runner since we were the second owners. It was also due to the fact that I wanted a 5spd 4Runner(missed my manual in the Taco) and those are really hard to find in my neck of the woods.

out:
I have done plenty of car work including engine/transmission rebuilds, motor swaps, etc so the thought of doing the 4wd swap wasn't scary. After being patient, I found someone that had a wrecked '00 4Runner frame/drivetrain that they were parting out 3 hours away. After some driving, I got the complete rear axle, rear driveshaft and the complete front section of frame from the transmission forward for $375!:rockon:
After disassembling the donor parts from the frame and my 4Runner, it was all pretty much plug and play. You do have to cut the floor to install the new 4wd shifter asy since the 2wd shifter is completely different. The next big modification is the transmission crossmember. I remember seeing that the Trail Gear Tacoma single transfer case crossmember worked on the 4Runner from a SAS build on pirate4x4 so I ordered one up. Pricey but it was bolt on and now I have some extra underbody protection after cutting out the stock crossmember. Just had to measure twice before drilling holes in my frame. You will also have to modify the exhaust bracket that attaches to the stock crossmember. Just heat and bend to connect to the frame instead.
Also, most of the wiring is there for the 4wd lights and relay. After tracing wires and studying the wiring diagrams(I paid the $12 for a 3 day pass to the Toyota Tech Info site and downloaded what I needed), I only had to attach/solder 5 wires! The 4wd light works and the front diff engages. I didn't bother with all the other transfer case switches since they aren't really needed. You only need to connect wires to the 4wd position switch to engage the front ADD actuator.
And yes, the 4wd drive works like it should and my 4Runner still drives just fine. The transmission plugs are identical between the a340e and a340f so it shifts like it did before. It just has a transfercase hanging off the back. The only thing that I haven't fixed is the speedometer. It is driven off of the abs sensors so going from 235/75R15's to 265/75R16's makes it read about 5 mph low but I can live with that at the moment.
All in all, it took about 2-3 weeks since I did the majority of the work myself. Plus, I did new rear axle bearings/seals and new upper & lower ball joints which added more time. Probably could have done just the 4wd swap in two full weekends with some extra help.
Final tally on money spent was around $800. Was it a good amount of work, yes. Would I do it again? Absolutely! If you can't find the right 4Runner to buy, build your own!
Sorry for the novel...... but do it! :bigok: You won't regret it.