I just did this last summer.    I called PPS and faxed in the Form 56, the court order assigning the administrator of the estate, Form 8821, and the death certificate and was able to get W&I transcripts.

The first rep I spoke with told me they couldnt take a faxed from 56, mail in only....but I called back a second time and the next rep accepted what I had.

You are on target.  This is the way to do it!