Hi Paul ,
Not sure what your exact requirement is.
Communication structure for E1 : KOMKBE1(VEBELN is your Inb Delv Number), You can use User Exit EXIT_SAPLVCOM_003 for manipulation of data .
For EF : KOMKBEA. Unfortunely the PO number is not available. You can use User exit USEREXIT_KOMKBEA_FILL instaed of. COM_EKKO-EBELN is your PO Number. You get the line item in COM_EKPO structure
In order to debug, you can put a breakpoint. Use Processing Medium as "1" in your Output and then run RSNAST00.
R