Well, I have just done a trawl through my logbooks for my time on 105 Sqn (1966 - 1968) and I can see no sign of XP444.
The Argosy website gives XP444 as:
28.11.62 Delivered to 267 Sqn at Benson.
01.07.63 To 215 Sqn in Changi.
15.01.68 To 70 Sqn in Akrotiri (NEAF) as a VIP aircraft.
03.11.75 Flown into Halton and scrapped in 1988.
For the record, the 105 Sqn Argosys during my time were:
XN819, XN820, XN849, XN852
XP408, XP409, XP410, XP411, XP412
XP437, XP438, XP439, XP440
XR109
I have a vague memory of XP437 carrying JEJ's pennant at one point but that is all it is - a vague memory.
I also remember the topsoil and manure as being carried by Beverley.