First try using clover boot screen menu, hit the right arrow on keyboard until you get to options.
Open options and go to graphics settings, enter ATI fake ID 0x67EF1002. If you have a EFI Backup folder on main partition check the config.plist using Xcode or clover configurator by dragging the plist to desktop and then opening with either of those. Check to see that thenfake I'd numbers are either zero or edit them with 0x67EF1002 do not use EDID, or inject ATI, just set the fake ID first. If it doesn't work try the same and inject ATI.
If that doesn't work there is a info.plist edit that is another option which requires editing the info.plist in the AMD4100kext in System/Library/Extensions. Right click on the 4100kext and choose "show package contents", drag the info.plist to desktop and open using Xcode go to IOKitpersonalities and open. Behind or after the 0x67EF1002 leave a single space and then enter 0x67DF1002. Hit save, close XCode and then drag the info.plist from desktop back to the contents folder. You should get "authenticate" and "replace" prompts. Then a password.
You're not done yet, don't reboot, now you need to run kextwizzard, not kextbeast it won't work, and select System/Library. Reboot and see if you have acceleration which you should know during boot if your fans rev up. Go to about this Mac and check for metal support.