everything except the mobo and cpu can be reused.
the gfx card will work, just not with dual monitors oob, and you cant install osx with it connected (install using onboard gfx, then plug in the 6850 once complete).
wouldnt it be easier to simply type AtiConfig=Duckweed AtiPorts=4 at the bootloader stage, rather than point to which config.plist you want loaded?
then you could confirm which framebuffer is being used with the "ioreg | grep ATY" command in terminal
try with the chameleon trunk as well as chimera. i found that with chameleon, my gfx card is...