FORBIDDEN WORLDS (vol. 1) #136 (July, 1966). Cover by Kurt Schaffenberger.
A mad scientist has created a robot-double of Magicman to commit crimes. Everyone now thinks the heroic Magician has gone over to the dark side, and it's up to Nemesis to stop him!
Writer/editor Richard Hughes definitely stole a page from Marvel Comics - their books were full of heroes fighting heroes - with this story pitting American Comics Group's only two superheroes against each other. And you can't blame Hughes, because Marvel's popularity was growing by leaps and bounds at the time, while ACG's - to put it kindly - wasn't.
Kurt Schaffenberger did a fair amount of work for ACG during this time period, usually to help out his old pal Pete Costanza (who is credited with the art for the cover story). Schaffenberger and Costanza met while working at Fawcett Comics during its heyday.
However, the bulk of Schaffenberger's work those days was at National/DC Comics (he was the artist on Superman's Girl Friend, Lois Lane, and filled-in on other Superman-related titles). And moonlighting at another company was a sure way to be fired by DC's editorial staff.
So, to get around that, whenever Schaffenberger signed his work at ACG he always used Pete Costanza's name.