Basically you can use any smbios . Thing is : Ati 4670 mobility is in iMacs of late 2009, therefore a SMBIOS of iMac9,1 - 10,1 will auto-enable graphics-energy-saver settings. But I use MacBookPro5,1 because it works best with my Core2Duo speedstepping ( I don't use any longer nullcpu.kext ) - my MBP5,1 smbios will conflict with the Ati graphics-energysettings ( AppleGraphicsPowermanagement.kext ) , so I always edit this AGPM.kext in that way that I rename all instances of iMac10,1 to just MacBookPro5,1 ..
To make the Graphicscard "just work" and do so with QE/CI enabled the above details are not important. It is all about Powersaving/Eleminating the loud fan noise from the GPU..
It will work as long as your device id is 9480 and have a display that outputs via Laptop standard - LVDS ( not VGA, not DVI , not Displayport ) .