Dick Giordano in an email to the indexer has confirmed that he inked this cover, and suspects that he pencilled it based on a layout from Carmine Infantino. However, it also seems to have a Curt Swan look; particularly Captain Cold.
Art credits as listed in The Comic Reader #191 (definitely Heck pencils). This story follows closely the events as described in Flash's first appearance in the first story in Showcase (DC, 1956 series) #4.
Writer credit from Bob Rozakis via Tony Isabella's blog.