Thanks for this great question. It is not covered in the Interim Manual, but it is covered in the new rules that have not yet been adopted by BANA. Because there is no current rule on this, we are authorized to use this new rule with the understanding that it might be different in the final adoption. Your transcription is considered correct at the time it was transcribed, so don't worry about it.
For that beginning dash, which indicates the beginning of a dialog, use the compound hyphen (25, 25) and follow it unspaced with the double dash (36, 36, 36, 36) for the blank to be filled in.
List the compound hyphen as a special symbol. You don't have to explain the usage, but just list it. The reader will see how it's used in proximity to the dash.