Here we go, i found the answer....
it IS a 2nd gen 12 bolt, they only made a 12 bolt in the 1970 second gen which came with the 396, every 2nd gen year after that got a 10 bolt.
http://www.nastyz28.com/camaro/zsusp.html
Camaro Rear Axle Information
The 1970 rear end differs from the 1971-1981 rear end. In 1970 the rear end was built in both 10 and 12 bolt versions. In 1971, GM instituted a standardized "corporate" rear axle. This rear end was available in a 10 bolt version only. The 1970 12 bolt version will bolt into any second generation Camaro and quite often is done so in high power applications.
Three piece housing includes integral cast iron differential carrier and housing with pressed in and welded steel tubes.
Semi-floating forged and heat-treated axle shafts. Wheel drive flange is forged integral with the axle. Axles are the same length for both sides
.
Differential carrier contains hypoid overhung pinion and ring gear. Drive pinion supported by two taper roller bearings.
Rear Suspension - Salisbury rear axle with multiple leaf springs.
Staggered shocks, right side shock is located in front of axle tube and the left shock is located behind the axle tube. This controls wheel hop.
Leaf Springs - All leaf springs were 5-leaf design, 56" long, 2.5" wide.
See yearly info for specific specifications.
Physical Dimensions
1970 10 bolt 1970 12 bolt Corporate
Bolt Diameter 3/8" 3/8" 7/16LH
Ring Gear Dia 8.20" 8.875" 8.50"
Pinion Dia. 1.438" 1.625" 1.625"
Axle Splines 28 30 28
The following dimensions are consistant across all 3 style rear ends.
Axle tube flange to axle tube flange: 55.25"
Between centerlines of spring seats: 45 3/8"
Axle shaft length: 30 5/32"