Jean-Marc Lofficier, Keith Giffen and Bob Oskner send Superman to ancient Gaul in Action 579 (May 1986), where he encounters two men who are not Asterix and Obelisk, but as close as they could be without violating copyright.
The story begins as Jimmy Olsen destroys an ancient shield while stopping thieves at a museum.
The story then shifts to Gaul, with a wizard character that I think is much like one from Asterix and Obelisk, though I confess I was never a fan of those books, and don’t know it well enough to be sure of all the correlations. At any rate, the wizard casts a spell, using the shield, to bring a great warrior from the future to help them, which pulls Superman to their time.
Giffen excels at portraying Obelisk, without actually showing him clearly. There is no other character it could possibly be.
And I can tell that the overall look is right. The people I knew who did enjoy Asterix and Obelisk just went nuts over this story.