I'm not familiar with "Walker's Carnivores", but the 1999 (sixth) edition of “Walker's Mammals of the World” lists the clouded leopard as Neofelis nebulosa and the marbled cat as Felis marmorata.
The section on marbled cat does state, though, that some authorities consider it closely related to the clouded leopard; while the clouded leopard section comments that Corbett & Hill (1992) place in with the marbled cat in Pardofelis.
"Walker's Carnivores of the World" is a 2006 re-release of the carnivore chapters from the 1999 (sixth) edition of “Walker's Mammals of the World”, edited and updated to some degree, which states the same in this regard as the excerpts you mention from the main work - these references being what I was thinking of.
