Many thanks, once more, bazv.  I think it was the extent to which it stuck out from the fuselage on both sides that I found unusual.  Maybe, from your knowledge, it was not so unusual but, to me, it was, so I am grateful for your help. 

Graham, I have found nothing specific to indicate that AL614 was involved in any kind of  trial. However ………

……… It was “off the road” in Dorval for the whole of March 1945 and a few days either side. During this period, there are references to “mods” but nothing specific.  Perhaps there are archives in Canada that could provide an answer.

Meanwhile, there is apparently a photograph of AL614 in the Oughton book on Liberators, which I do not have. My note says it’s on Page 112. If anyone has the book and could post a scan, it would be interesting to see if it has the appendage in question.