Remove the large nut & the flange.
The drum should slide off like a rear drum.
Than you can remove the bolts holding the backing plate to the rear housing.
Here is a youtube link that shows how...
https://www.youtube.com/watch?v=0q-p0CVL6nA
If you are looking to make this 475 a slip yoke car style trans, you need to change the entire output shaft which requires dismantling the trans.