I just did this last week in my 2004 when a guy on CL was selling some Weathertechs from his 2012. The fronts and the second row pieces fit great, almost exact. The cargo/rear "mostly" fits. It is about 1-2 inches short of the depth front to back while the width is just slightly too wide. But it is close enough considering the price vs new.
Here is what they look like. (Don't judge me on the cleanliness. I got this 4Runner for a decent price due to the interior.
)
Front:
Second Row:
Cargo (The mat is on top of the lowered cargo deck or whatever it is called):