While putting together a tribute to the late Jeff MacKay, I tarried in the episode guide for 'Tales Of The Gold Monkey'. And according to the back-story, Ron Moody originally played Bon Chance Louie in the pilot for the series. However, there were "differences of opinion" between Moody and the producers about how the role should develop and be played. So for the series itself, the late and legendary Roddy McDowall was brought in to play Louie. (And according to MacKay, McDowall brought real class to the role.)
As much as I have enjoyed Ron Moody in the few productions I've seen, Roddy McDowall would always win out [in my opinion] as the real Bon Chance Louie. I'm that big a fan. However, I shouldn't be playing favorites with the Toobworld concept. (Although, let's face it, I do!)
Therefore, Ron Moody must be considered the true Bon Chance Louie. So a splainin must then be found to satisfy Toobworld's inner reality as to why Roddy McDowall was a recastaway.
I'm tossing out plastic surgery right away. For the times and the location, surgery of that sophistication would have been impossible. They would have been performing 'M*A*S*H'-quality "meatball surgery" (and not even on a par with the "skills" of Frank Burns!) on those islands.
Another possibility that came to me would have been Dr. Jonathan Willoway of 'Fantastic Journey'. He could have found a dimensional escape route and used it to save himself. And having once arrived back on Earth Prime-Time in 1938, he would have dispatched Louie and taken his place.
But he was a bit of a con man and something of a coward, and I don't see him staying long there. There were too many other con men and thieves all around him at the Monkey Bar, and not enough chance for making a fortune for himself.
There's only one character he could be - Edward St. John V, from the 'Quantum Leap' episode "A Leap For Lisa". In that storyline, Dr. Sam Beckett leaped into the life of a much younger Al Calavicci, which caused a disruption in Al's personal history. And until Sam could fix the problem, the future history was also altered so that Al was no longer his personal guide through the past. Instead, he was replaced by Edward St. John V, who had no clue who Al Calavicci was supposed to be.
We know from other episodes of 'Quantum Leap' about that evil Queen Bitch leaper that the technology for leaping would be greatly improved so that a leaper could pinpoint their destination and have control over it. So I'm thinking that Edward St. John V, who probably worked on the Quantum Leap Project staff regardless of Al's fate, eventually was called upon to accept a long-term leap assignment....
He was probably asked by the government to step in and replace Bon Chance Louie, for at least the duration of the coming World War II. The idea could have been that this operation would ensure that History in that region would continue on its prescribed destiny. As the original Bon Chance Louie had been a thief sent by the French to keep an official eye on other thieves, I'm thinking the "Timecops" of the future couldn't take the chance that Bon Chance would hold up his end of the bargain.
So Roddy McDowall may not have been the original, but his character of Edward St. John V proved to be the better Bon Chance Louie.
[My thanks to Al's Place, a 'Quantum Leap' website, and the 'Tales Of The Gold Monkey' fansite for their unwitting contributions to this piece.]