The signature on the cover appears to be of Clinton Spooner (1913-73), who was a pulp artist. The signature is different from those found elsewhere online, but has the characteristic dash flourish at the end which appears in all his signatures (all of which look different from each other in other aspects).
On the inside front cover. Signature noted by Ger Apeldoorn via the GCD Error Tracker.
Letterer credit comes from reprint in Doc Weird's Thrill Book. [MN 3/2008]
Signature noted by Ger Apeldoorn via the GCD Error Tracker.