Well!
I have only read through that once so far, but will do so again.
But the thing that occurred to me from your first post was to wonder how likely it would be for Rupert Henry (a Clerk normally dressed in a navy suit) to become a seaman and then a steel worker. (as per Lassiter) And I see nothing at first read to make me un-wonder that.
The weight of evidence as you have outlined it does seem to be on your side rather than Eddy's. BUT, the other thing about your story is that - wasn't James Francis WALL born about 1910? To leave an orphanage just before he turned 18, then turn up to marry in 1933 only leaves a 5 year gap. and he wold only be 23. That seems rather unlikely too!
I might have mis-understood - will post this anyway and consider.
You have a major grasp on the situation!
Its that 5 years I cannot trace either of them. Rupert went missing in 1929 and is 10years older. James ran from the orphange and reappeared with tales of adventure.
I didn;t make myself clear at one point so sorry.
Rupert was a friend of a famous fiction writer at the time who wrote books (Zane Grey? not sure) of a Jack Lassiter who had the self-same adventures.
Eddy thinks Rupert skulked off to Tasmania which is where John Lassiter claims he was born.
It is unlikley that Rupert is an interloper into my family. I am sure the Wall brothers would have known him to be an imposter!
But... Rupert's family and friends have ties with Gosford where John Lassiter's wife was born.
My James as far as I know has none.
Gladys Dillon lived in Sydney. At one stage I suggested she knew Rupert who came from money, met my James and they bumped him off! Eddy actually thought it was feasable
Perhaps they went to sea together, travelled to America, and or panned for Gold in New Guinea and one was left behind?