Does an 86 IROC Z-28 come with a posi rearend? Also, I am wondering if i should put in a new tranny. I just bought the car and the guy i bought it from put in a modded 350 (headers, headwork done, edelbrock intake, holley carb, no cat) and i am wondering if a new tranny to replace the stock one would be a good idea. The car has 54,000 miles on it and the new engine has 1,500 miles on it.
Thanks

 

Does that mean it was stolen?

Being a Z doesn't say anything about it having posi. You need to check that out yourself, either by finding the 3-character code stamped on the front of the passenger side axle tube and looking up the code in a book like Haynes, looking for a posi tag on one of the cover bolts, running a "posi check" (with rear jacked up, park brake off, trans in park, try to turn one wheel by hand - if you can turn it, no posi or it's shot; if you can't turn it - posi), or pulling the cover and looking (springs and plates = posi; spider gears = open).

You probably don't need a new transmission just because it has a 350 now, but a Transgo shift kit would be a good idea to help it handle the extra power.