i bought a 4runner with 36" tires on it how would i find out if the stock gears have been replaced with out taking out the 3rd member?

Jack up the rear pumpkin, Turn the tires 4 times, How ever many times the Driveshaft spins is your gears.

So in that case...you turn your tires 4 times, The Driveshaft spins 10 times, You would have stock 4.10's...
I believe that is the crude way of checking...

does it suck ass on the road? if so it has stock gears