AceShowbiz - Comedians Will Ferrell and John C. Reilly are forging ahead with plans to record a rap album after landing a "big time producer" to collaborate with on the project. The "Step Brothers" co-stars have previously toyed with the idea of releasing a joint music project and entertained fans with their rapping skills on spoof songs like 2008's "Boats 'N Hoes", even recording a video and posting it on YouTube.com.

But the plans have now been put into motion, according to "Step Brothers" director Adam McKay - and they're hoping to entice hip-hop star Mos Def to join them on a track. McKay writes on Twitter.com, "I wasn't kidding about Step Bros rap album. And we just found out we have a crazy big time producer. Mos Def, you up for a guest flow?"

The filmmaker has yet to reveal the identity of the mystery producer. The rap disc won't be Ferrell and Reilly's first foray into the hip-hop world - they both feature in "Fight For Your Right Revisited", a new short film about iconic rap group the Beastie Boys.