I spoke to the chap at the Museum at Manston about this having seen the tip of the chopped off prop and it described as off Pegwell Bay. So, here's my memory being dredged up.
I grew up in Sandwich, born late 1950s and remember trudging out what we regarded as a bomber, Certainly 4 engines and at very low tide you could see the cowls of the engines and walk on the wings and the fuselage. If I was to try to guess at what plane, I would have said a B17, possibly on its back, I just can't place a tail-plane, certainly not the twin tail of a Lanc. Also, the engine cowls (I'm stretching my memory back, but I was a boy who made many Airfix kits so knew one plane from another) didn't give the appearance of Lanc, more a B17. I remember walking out more than once and would place it (my father agrees) about 5 to 600 yards out and the same distance towards the mouth of the Stour from what was the old Guildford Hotel. I suppose pretty well straight out from the edge of the Bird Sanctuary. When I walked out to it back in the 60s, the props were still sticking up! I Think it was particularly well exposed after a very bad storm in about 1970?.