Omnibus of The Portal in the Picture [restoring the magazine title to Beyond Earth's Gates (1954)] + Valley of the Flame (1964) + The Dark World (1965.) All had original magazine versions in Startling Stories 1946 or 1949.

Beyond Earth's Gates (1954) - first appeared in Startling Stories September 1949 as "The Portal in the Picture." Under Eddie Burton's management the ambitious starlet Lorna Maxwell seemed headed for the top of Broadway's glamorous world of make-believe. And then she vanished - through a wall where there was no door. Eddie found himself plunging after her into a city beyond reality. They find themselve in a weird twin to New York, ruled by an evil theocracy - to whom our Earth was "Paradise."

Henry Kuttner's Valley of the Flame, in its first book appearance. The magazine version appeared in Startling Stories March 1946 as by "Keith Hammond." Most sources consider C. L. Moore to be co-author on this. Since their marriage in 1940, almost anything they wrote had some element of collaboration, particularly when using pseudonyms... the style and type of story fit, too. It's been decades since I read this story - I'll have to quote from the back cover:

Deep in an unexplored jungle, Brian Raft sought the secret of the legendary VALLEY OF THE FLAME. Somewhere there was a radioactive fire that could perform miracles of super-science. Somewhere there was a place where cat-people prowled, where time was altered, and incredible mysteries held their secrets of power and fortune for the daring discoverer...

Henry Kuttner's: The Dark World - the magazine version appeared in Startling Stories Summer 1946. It's been decades since I read this story - for an idea of what the book is about, I'll have to quote from the back cover of the 1965 Ace paperback:

It started when Edward Bond was visited in the night by a giant wolf and a shadowy hooded figure, and felt the compelling call of the Need-fire. Or, perhaps the real start had been eons before... Bond was thrust into a strange other-world which had branched off from his own Earth thousands of years ago - a world where an ages-long battle of science and sorcery still raged, and where Bond himself was in some mysterious way the focus of powers and forces beyond his imagining.