Hi guys can anybody help me ID my 12 bolt especially the gear ratio.
it came with my 70 cutlass SX
see pics.

 

That rear looks like possibly the original 12 bolt Olds. It's a 2.56:1 anti-spin.

 

The tooth count for the ring and pinion gears are stamped (engraved?) in the perimeter of the ring gear. Just divide the larger number by the smaller number to get the ratio. I can't read that well but 16 A 41 is a 2.56 ratio.

And yes, an SX would likely have a 2.56 gear as standard equipment.

A picture of the casting number on the bottom of the pinion snout will ID the type and year of the rearend.

 

Read the ring gear. 41÷16= 2.56:1