[David Bates]

Looks like an 8.2" 10-bolt.

 

[123pugsy]

8.2

The 8.5 has triangular "ears" at 5 and 8:00.

 

[captpn]

Lots of details here:

Generic Rear Axle Info

Decoding Chevrolet VIN, trim tags, cowl tags, engine, engine block casting numbers, cylinder head casting numbers, intake manifold casting numbers, transmission, interior codes, and paint codes.

chevellestuff.net

and

1971 Chevelle Rear Axle Codes

Decoding Chevrolet VIN, trim tags, cowl tags, engine, engine block casting numbers, cylinder head casting numbers, intake manifold casting numbers, transmission, interior codes, and paint codes.

www.chevellestuff.net

Looks like a 10 bolt to me however you didn't show a pic of the axle tube codes. Check out the links.

 

[Hotwire]

If you have posi traction, chock front tires, put car in neutral, disengage parking brake, jack both rear tires off the ground, mark pinion and bottom of tire. Rotate tire 1 time while counting how many times the pinion turns, if 3 3/4 turns, you have 3.73s.

If open diff, chock front tires, put car in neutral, disengage parking brake, jack 1 tire off ground, mark pinion and raised tire, rotate tire 2 times and count pinion turns. If 3.73 pinion will turn 3 3/4 turns.

 

[1967LSxChevelle]

It’s an 8.2. Most 8.5s have cast in lugs at 5 and 7 o’clock. Another easy way to tell is by the pinion nut size. If it takes a 1.125” socket, it’s an 8.2. If it takes a 1.25” socket, it’s an 8.5.