The other problem is that the Marlowe in the 50s books is clearly different from the character we all enjoy in the books up to and including THE LITTLE SISTER (Garner clearly not up to the caustic side of Marlowe in the film version). That had to be addressed in any version of THE LONG GOODBYE, and Altman obviously took it to an extreme. One message in Altman's version that we may not want to cop to but that is probably right on the money: a present-day (70s or now) Marlowe would not be up to snuff, tough-guy wise, with the bad guys he was up against. That's where the wily side of Gould's performance really works, even if he's all-too-alien in the role otherwise.
Bottom line there's no way to get back there from here without it seeming too obviously retro in conception. Who could play a satisfying Marlowe now?