UK Direct Debits in R12

I see that Oracle have recently posted a couple of documents on customising Funds Capture Settlements (1325613.1 & 1287827.1).
These are all very well, but they give no indication of how to link from the IBY_TRXN_SUMMARIES_ALL table to RA_CUSTOMER_TRX_ALL.

I need to do this to be able to get to the IGI_RPI_STANDING_CHARGES_ALL table to derive the BACS transaction code (01 for first Direct Debit, 17 for subsequent ones).

Can anyone help - or do you have an alternative way of getting the information?

Thanks

Ian