Adam,
From memory the width is 1420mm which is the same as the Sprinter rear ends. It's a straight swap in width for the Sprinter rear end anyway according to a mate who slotted one in his rally car.
They are leaf rear end but either way you would have to put your own mounts on it to install in a Celica.
The diff came from a 89 RWD ute from memory. I bought it from a local wreckers who specialise in commercial vehicles. All the bearings etc are fine. It's a drum brake rear end but the brakes that come with it as a package are the discs and calipers from a Sprinter.