My 72 SS has a 12 bolt rear end here is a pic of it I've never seen a set up with these springs what do i have?

 

It's an Eaton limited slip differential, that's what came in the 12 bolt from GM.

 

and to get my gear ratio count the teeth in the ring and devide that number from the teeth of those pinion gears right? How is that Eaton set up i cannot decide ìf i should install a locker or not what are everyone's thoughts i would like to have 3.73 max gear ratio

 

I'd run that Eaton,its a good solid piece,unless you are going drag racing a lot with big horsepower it should be fine as is.
Yes divide pinion gear teeth into ring gear teeth to get your gear ratio.

 

Most ring gears have the number of ring and pinion teeth stamped into the end. Rotate it around until you see the numbers, then you won't have to waste time counting.