AUA is a 55 kW engine. The similar 55 kW engines that equipped lupo (with the same manual gearbox 085E code FFR or ETD) are: AHW, AKQ, APE, BBY. AUD isn't a 1.4 16v 55kW motor. It is 1.4 8v 44kW engine.
I think the most similar with AUA is APE (the wiring diagrams are identical, the same ECU's Magneti Marelli 4AV). AHW and AKQ are the older generation (with only one oxigen sensor), ECU's and wiring diagrams aren't the same with AUA, and BBY is a newer version with two oxigen sensor but with individual induction coil (the same story like AHW and AKQ from the point of view of wiring diagrams and ECU).
The conclusion is that the best fit is an APE engine for a direct replacement.