THIS IS IT! THE CROSSOVER YOU'VE BEEN WAITING FOR!
Among the highlights of Destroyer Duck #1 was a backup story by friend of Steve Gerber, Sergio Aragones. It was Groo The Wanderer, a take-off of Conan The Barbarian. Groo has survived since then, landing at Marvel's Epic line-up and Dark Horse and just generally keep on keeping on. And occasionally you'd see someone on a message board say there was a Groo/Conan crossover in the works, only to later say they were just kidding.
They ain't kidding anymore.
There is going to be a Groo/Conan crossover. It will be published by Dark Horse. Here's the cover.