Can anyone say what is this rearend?
Gear ratio is i believe 2.56
Previous owner told that it is HD rearend.

9.375 Olds 'O' type?

 

Hi,

There is a code on the front side of the axle tube on the passenger's side of the car. You may have to scrape off some crud and/or undercoating to see it. You can decipher the code in the service manual. If you don't have the manual, post the code on here and somebody will be able to tell you which rear it is.

Is your car registered on the '75 Olds 88 Convertible registry?

http://www.1975oldsmobileconvertible.com/

 

That is what I call the "large 12-bolt" It' is a 12-bolt cover,with a big 12-bolt ring gear.This is not the same as a 12-bolt Chevy,12-bolt Truck,or 12-bolt O-axle.
What car did it come out of?

 

76 Regency No i have not registered.
507OLDS it's from my´75 delta88royale 455

I'll have to check this code thing, thanks for advice.

 

You should definitely register your car. If I remember right, there were only a few hundred 455 models. Yours being out of the US makes it even more interesting.