How to Upgrade/Replace GPU Graphics Card on Mid-2011 21.5" iMac - YouTube
2GB Graphics Video Card HD6970M Replacement, for iMac Mid-2011 27 Inch A1312 Desktop PC Computer Core i5 MAC814LL/A MC814, AMD Mobility Radeon HD 6970M GPU Upgrade MXM Board Repair Parts
Original Graphics Video Card GPU Upgrade Replacement, for Apple iMac 21.5 Inch Late 2011 Core i3 3.1 All-in-One Desktop PC MC978LL/A, AMD ATI Mobility Radeon HD 6750M, MXM VGA Board Repair Parts:
iMac 2011 GPU upgrade to NVIDIA 770M with new VBIOS - YouTube
2011 iMac 27″ K1100M Graphics Card Swap And Install Catalina – TuXxX Blog