What you are describing is a Corporate ten bolt rear out of a 1972 and up full size car though the 5 on 127mm bolt pattern tells me it is a 1985 or newer police car or a 1994-'96 Impala SS as the donor vehicle because the standard duty still used a 5-4¾" bolt pattern. Studs are also metric 14 by 1.5.
This is good because the standard rear had a 7.6" inch ring gear. The HD corporate rear was usually a posi (though not if it came out of a cop car) and had 30 spline axles. That makes it nearly as strong as a a 12 bolt. The Impala SS had disc brakes front and rear.
In inspection cover is there to allow you to look inside. That way you can see the size of ring and pinion and the condition of the parts. It will also reveal if it is a posi or not.