Link from VBAK to EKKO?

I do not believe that there is any way to link VBAK to EKKO but I thought I would ask. Basically what I need is to display the PO/Sales Order number if a delivery was created off a STO verses a Sales Order. The only place that I can think to get the PO number is EKKO. However how would I grab EBELN (PO number) for a certain delivery number?

Regards,

Davis