Nice account; I did know all that--I've heard Hunt talk of this (I had him sign my libretto), and, like you, I also have researched the show extensively.
What I was curious about was keeping the severity of his condition a secret.
Do you have a source for "pneumonia"? Because I found newspapers listing virus, Hong Kong flu, and "undisclosed" illness.
PS--it's also interesting that in Ostrow's memoris, he mentions Drake's convincing Da Silva to return, but says Drake had seen the show with Everhart and that he got more laughs as Franklin without the "Doozy Lamb" scene. Ostrow makes other errors, so I'm more inclined to go with the eavesdropping Hunt. But it's a nice example of how history gets written.