Hi Andy,
In our case, B2B adapter actually transforming the EDI message to an IDoc XML file (DESADV.DELVRY03). Now PI is picking up the file through File Adapter and we have used below:
File --> Sender Interface: DESADV.DELVRY03 (Though we are not receiving ALE IDoc but IDoc XML, but we can use IDoc Structure as our Sender side, you can import DESADV.DELVRY03 from ECC just to use the structure)
Operation Mapping (XSLT Mapping provided by SAP): DesadvDelvry03_DespatchedDeliveryNotification_01
ABAP Proxy --> Receiver Interface: DespatchedDeliveryNotification_In (Already available with SNC Standard Content within PI, you need to activate the Proxy at SNC side).
Regards,
Nabendu.