The sound engineer at the Trades club was Vince Robson (deceased 2005), a suspect in the unsolved murder of Tina Bell in Billingham, North East England, 1989. Robson was a friend of Billy Dunlop also a suspect in Tina's murder, the first man to be convicted ( murder of Julie Hogg) under double jeopardy law in England.
To weigh a body with a big rock & carpet & dump in the canal suggests the use of a boat & very likely a second person.
I've seen Christopher Halliwell mentioned in this case before, he was a keen fisherman & narrow boat owner & enthusiast with an extensive knowledge of British rivers & canals.