I've seen a few 4Runners rocking 35's with "minimal metal work by tapping the corners in with a sledge. The amount of metal work depends on the tires you get, not all 35x12.50 have the exact same dimensions.
If you don't want to limit up travel then you are looking at metal work for 35s. No way around it. Besides a ridiculous body lift that I wouldn't suggest to my worst enemy.
35's are a big step for an IFS truck. The extra weight of the tires puts a lot more stress on the bearing, suspension and drive train. So then it starts... you might need new UCAs to clear the wide tires, wheel spacers, new wheels, lower gears, trans cooler, bigger brakes....
I personally love my 35s. My road to 35s cost around $3k in parts all said and done with. $1600 tires, $300 Tundra brakes, $250 Wheels, $700 UCAs, $100 spacers and some other odds and ends, sure I'm forgetting something. A year into beating it up and wheeling out in NorCal earned me a couple busted teeth on the front gear. $3k later I had an ARB up front and 4.88s. And a $1500 TRD S/C to help lug the little bastard up these hills.
+side of 35s - obstacles can be negotiated at a slower speed (usually), extra ground clearance, more aggressive tires in the 35+ category and it just looks a hell of a lot more beast. I could explain the huge difference I had between my 33 Kumos and my 35 Pitbulls, just night and day. Check out the vid
I'm not trying to deter you from 35s. I'm encouraging as long as you're comfortable knowing what you're getting into. Here's a link to the 4Runners on 35s thread. Front end is basically the same but you should have less to worry about in the rear as the Tacos leafs don't flex as much.
http://www.toyota-4runner.org/3rd-gen-t4rs/108367-official-3rd-gen-4runners-35s-pic-thread.html