Ibelieve your washer is thwe same as the Matag neptune machine.http://www.applianceaid.com/neptune3.html#belt
If i remember correctly,the motor is on a spring loaded pivot and you just stretch the belt over drum and pulley. If it is neptune type I'll see if I still have a manual for this.
I used to work on some of these at a commercial laundry.Pumps were the biggest issue with a stray bra underwire on occasion.
Are you sure the tub bearing is okay,does it spin when you tubn it by hand from inside the door?