Just what I was thinking. Mine is probably the most sensible and constructive post on here IMO!!

Just take it to someone who knows these engines mate. Chances are it will be diagnosed in 2 minutes properly. Fairly sure one of the big Skyliner tuners would have heard a knocking bottom end before on one so will give you an answer.

Personally I would be doing that 10 times before even thinking about dropping engines out or taking the sump off etc.

Like I said. Hope you get it sorted.

EDIT: Just seen you have taken it 3 places already and had 3 differing opinions. Thats a bit more worrying I guess.