I believe that's Denny Conn's recipe for Rochefort 8.
I'm not certain if the 6 and the 8 use the same grist but I imagine it's possible. They might use different yeasts or fiddle with fermentation temperatures or something too. I'll go look it up in BLAM and see if there's anything in there....
Update: BLAM (Brew Like A Monk) states that the grain bills are about the same for 6, 8, and 10, with extra malt and sugars in the 8 and 10. The difference, then, is likely a bit less malt and maybe little or no dark candi syrup. Rochefort 6 is also stated as 20 SRM versus Rochefort 8 having 32 SRM, and 1.072 vs. 1.078, which seems to support this. So, maybe use the same recipe but aim for the specified OG of 1.072 with no dark candi and 20 SRM and see where that gets you. If you need to reduce color further to hit 20 SRM, I might take out some of the Carafa, but leave the rest alone.