The culprit responsible for butchering Kline (and other writers) was the editor at Avalon Books. Don Wollheim, editor of Ace Books, said that he was unaware of the editing and simply reprinted the Avalon editions.
I liked the Kline Venus trilogy when I read them as a teenager (the first two in the damnable Avalon edition), and would love the opportunity to reread them in an unabridged form. By the way, one can't presume that the McClurg editions weren't abridged from the Argosy versions. Burroughs' Moon Men and Merritt's Moon Pool were both longer in the Argosy serializations. (As I'm sure you know, book publishers sometimes are concerned about length, having to maintain their budgets.)
Indeed, a reprint from Argosy of Moon Pool/Conquest of the Moon Pool would be appreciated.