Mike,
Just wondering is you actually tried to put 16 inch wheels on your 4Runner and they did not fit or were told (by say a tire store, etc) they would not fit????
If the answer is the former then you may have been given incorrect information. If it is the latter and a previous owner did not modifiy the brakes, then Toyota made changes.
When I was shopping for snow tires a couple of years back the Tire Store told me that the 16" wheels would not fit my 2004 SR5, 4WD 4Runner.
FYI, these wheels were from a Tundra. I told them to pull one of my 17" wheels off and see for themselves.
They learned that day that their on-line system and reference books did not differentiate between the 4Runner models that could and could not run 16 inch wheels.
Their system and books said ALL 4Runners could not run with 16 inch wheels. Needless to say, after my visit, they made a manual correction to the incorrect information.
Who knows, maybe Toyota did increase the size of the brakes on all 4Runner models at a point in time. Does anyone have a repair manual for later model 4Runners or spec sheets that specify brake sizes?