"If There Were No Superman" in World's Finest 38 (Jan-Feb/49) seems to have been a stumper as far as IDing the penciller goes. His final World's Finest Boy Commandos, as it happens, was in the previous issue. This is his second Superman story, the first being "The Man Who Bossed Superman" in Superman 51 (Mar-Apr/48); before 1949 is out he'll start contributing the occasional story to Superboy.
Curt Swan will return to drawing Superman.
The best guess on the penciller for "If There Were No Superman" has
been Wayne Boring, with a question mark. That just goes to show how
important it is to ignore the inking; in this case Stan Kaye's inks on
Swan immediately remind you of his inks on Boring. Try to
imagine these panels as if inked by George Klein. One way or the other,
have to look behind the inks for Swan's poses and layouts and a few
recognizable facial types. The less you look at Superman himself, where
Boring's version is certainly the model, the better. On other
pages than these, objects like castles and ships showcase Swan's
realistic approach rather than Boring's impressionistic one.
Speaking of inkers obscuring pencillers, that Boy Commandos story in WF 38, "Rip Carter—Fugitive from a Chain Gang," has been attributed to Swan, but its pencils are by another BC artist you've heard of: Jack Kirby.