You will need a new bezel around your radio (the silver, or dark silver in sport edition, plastic at surrounds the radio and ac controls) You will need the bezel for the 4runners that do not have the 6 disk. Other than that it should be plug and play, make sure you get the nav disk with it as those are pretty expensive.
You will need to tap into the Vehicle Speed Sensor wire behind your HVAC controls. This wire then connects to the center pin of the 5 pin wiring harness connector in the back of the head unit, if your unit does not come with a wiring harness for this it is easy to solder straight to the pin. Don't worry you only need to do this for the one wire, all other wiring harnesses are plug and play.
Scroll down to my lower post where I linked to a page with info about how to find the VSS. If you also want to hook up a back up camera you will need to do the same thing with the reverse sensor wire, (do a search).
Also if you want to do the backup camera I have a plug and play one I can sell you as my unit the (non-JBL) does not support it. I also have the radio bezel you need, I was planning on keeping it for a spare, but if you cant find one elsewhere may be interested in selling it. (you should be able to find them on eBay)