with out opening the cover is there any way to find out what gears are in my rear /its an open rear/i cant find out where to decode it .i seem to remember where i saw the info on it the only id #'s i can find is just to right of the cover oi see #'s 0171 i think. it's a 12 bolt can you steer me somewhere thanks

What vehicle?
check out the "Index to years"
http://www.chevelles.com/years/

That is if the guts haven't been changed.
I had a 12 bolt posi stamped for 3.31 and when I pulled the cover I found a 4.10

Look for an number-letter stamp on the forward side of the right hand axle tube. That should help if no one has changed the internals. Post that code in the "Tag Team" section of this site.

looked on rear axle tube and found nothing but i looked on the back side only.so hopfuly today i'll look on the frt side .if i find a code i will post it as asked to do . thank you for your help