Posi Rear End????

[Italia]

first of all.... my truck spins both tires when i do a burnout. i have been reading that a way to tell if your rear end has posi is to jack up the rear and spin a wheel. if the opposite wheel spins the same way.... then its a posi rear end. if the opposite wheel spins the opposite direction then it is NOT posi traction. so out of curiosity i jacked up the rear and spun the wheel.... the opposite wheel spun the opposite way.... so that would indicate NO posi right??? but both wheels spin while burning out and clearly leaves two tire marks and gets a little sideways.... i am confused now.

also what was the stock rear end on a 62' Chevy??? mine has 10 bolts and i dont know what gears.... thanks guys!