Mopar makes the stage 6. I had the stage 5 iron heads on my Prostreet Ram and they were nothing more than 906 heads. Waste of good money!
If you choose to change heads I would go with the Eddy's 88cc chambers or if you can find a good set of used B1 heads would even be better. I have been hearing bad things about the Indy stuff! My buddy ordered a set of roller rockers for his 426 Hemi and they are PURE garbage!!!! Chinese crap with no bearings or bushings in them!
I have a build thread on www.fastmopar.com too. Just forgot to tell you about it since it was a new site. Get with Josh over there and find out what head he is using. I think he owns that site. He has a badass Duster with a BB turbo setup among several other members. His was just in several magazines.. They are building their cars to run in the X275 class.
Just make sure you get 80+cc chambers or it will change the compression ratio!!!!!! That is unless you are removing the turbo.....