Lensman in the Old Phoenix. How would he have handled a Lensman novel - apart from writing it well?
The Series' Premises
Planets form when stars pass close enough to pull matter out of each other.
Therefore, many planets will form when two galaxies pass through each other.
The Eddorians have moved their planet between universes in search of many planets for each of them to rule.
They will wait in this universe until intelligences have evolved in the two galaxies.
The Arisians, already old in this universe, plan to thwart the Eddorians.
That theory of planetary formation is outmoded. However, a Lensman novel could be set in a universe where the laws of physics are such that planets form as described here. Smith's multiverse allows for the coexistence of different kinds of universes:
(i) stellar close passes generate stars;
(ii) the galaxy is the entire universe, surrounded by an infinite volume of empty space;
(iii) an expanding universe of many galaxies with planets round every star.
(i) and (ii), which could be combined, are based on early twentieth century cosmologies. In (ii), other "island universes" might be undetectably far apart in infinite space. Even if it were possible to learn in which direction to travel, an FTL generation ship might be necessary to reach the nearest. Poul Anderson would be able to make such alternative universes seem real.
He would have to do something about the Eddorians' psychology and motivations. All they want is POWER! (They want to be Larry Niven's Slavers.) Anderson analyzes alien motivations for interstellar imperialism in "Interloper."