68 cuda posi traction ??

If it's smokin both tires it's either a spool or a posi I would assume. Open rears don't smoke both tires. If you want to know for sure you would need to pull the inspection cover on an 8 1/4 or pull out the pig on an 8 3/4. Also you can jack up the rear end and spin one tire and see if the other rotates the same direction. If they rotate the same way it's probably a posi. There are a bunch of sites with info on identification.

try this one:http://www.autohobbydigest.com/8_75.html