I spent a day at the Will F. Jenkins (Murray Leinster) Collection at Syracuse and made some progress on these questions:
"Space Ferry" was a 'working title' for at least the third book in the series, which became "City on the Moon". Two radically different plots were considered for this book, one involving using an asteroid with a very eccentric orbit to 'ferry' supplies from the neighborhood of Earth to the neighborhood of Mars. The other plot clearly led to the book as we have it now. An early (not final) typescript describes SALLY HOLT arriving on the Earth to Moon "ferry".
Leinster had a dispute, ultimately involving lawyers, with the original publisher. The correspondence mainly gives Leinster's side, so the objective merits are murky (although I would bet on Leinster). But this certainly explains the delay in the third book and the change of publisher. No correspondence with the second publisher survives. Too bad, as it might shed light on the change from Sally Holt to Arlene Gray.
It is certain that Leinster did not forget that the earlier books gave the character the name "Sally Holt" since she appears under that name in the aforementioned typescript. Nothing in the correspondence with the original publisher indicates any discussion of an original name of Arlene Gray, changed at their request and changed back, eventually, for the third book after the change of publishers. It is a possible theory, but unsupported by any evidence.
I intend, when convenient, to visit the collection again. If anyone has approaches to these matters they would suggest I explore, I will try. And, of course I may stumble on relevant points as I research other questions.
The collection is a great resource. I have previously enjoyed correcting from typescripts misprints and an entire missing line in Leinster's "Operation Outer Space".
