do these cars have posi? sometimes my right tiremark looks longer than the left

 

Yes, these cars do have posi. It's actually called limited slip something, which is just a fancy name for it pretty much.

As far as why one of your tire marks is longer than the other, I'm sure it's not by much, but if it is...?

 

It is a limited slip differential.. basically what it does it applies power to one tire but if the power is so much that it is about to slip then it starts turning the other wheel too. It is a little different than your old style true posi tractions, but is supposed to be just as efficient in reducing wheel spin.