Due to differing opinions on this – I thought I would confuse the issue with some facts.

Please find the Lancaster drawings for IB and OB at the join with the wing and firewall..

As you can see the OB has the cranked bottom edge that extends into the front nacelle and so although the engines may be interchangeable the nacelles must be different at least at this rear join.

Of course this is just my opinion and any engineer with experience of the Lancaster is better suited to reply than me