Tight and square with flat spine; faint (almost) crease at lower left of back cover (which may not show in scans.)

You could consider this to be a modern revision of an Ace Double from 1962. Novel-length "The Long Warpath" is revised from Cache from Outer Space, and 2 stories from the collection on the flip-side of that Double are included to round out the book - "Rastignac the Devil" and "They Twinkled Like Jewels" (both from 1954 - originally in Fantastic Universe or Magazine of F&SF.)

[I haven't read the new version, so here's the plot/summary for Cache from Outer Space:
Benoni Rider set out across the unexplored desert of a future America to prove himself a man and to find a new land for his people. The task at first seemed merely exceedingly hard - and then it began to seem entirely impossible. Because all he had to do was join a barbaric army, become a bodyguard for a queen, act as another nation's emissary to his own, lead an army into battle against the wild men of the north, and manage somehow to get back to Fiiniks with the secret of the CACHE FROM OUTER SPACE. This last secret, if learned, could enable any of the barbarian nations of that devastated future to control the rest of the world - or annihilate it all over again.