Answer
The correct underlying view/presentation object to extend with custom fields for the Delivery Note report is the Customer Order Delivery Note report view — though its order-line-level details aren't specific to just that one delivery note. A working technique used successfully for a similar Customer Invoice-lines scenario: build custom fields that look up the Customer Order Reservation Lines associated with the despatch, and use LISTAGG to concatenate together the engineering change revision, lot/batch, and quantity for each one, since more than one reservation line can apply to a single delivery note line. Note a specific limitation here: even though Report Designer has a built-in Part Lot Ref sub-element, the standard _REP view's own data column doesn't actually include every lot reference that was picked for a given delivery note, which is exactly why a custom LISTAGG-based field built from the underlying reservation lines is needed to surface the complete picture rather than relying on that built-in sub-element alone.