Another great guide! I split my Fusion Drive and replaced the HDD with a 1TB SSD with no issues. Thanks!
These photos do not show this iMac's optional configuration that contains a discreet GPU. If a GPU card is present there is another Torx screw that must be removed that holds an additional heat sink to the upper right corner of the enclosure. Note that in this configuration, the optical drive fan has a different configuration with a plastic separator that points towards the top of the iMac. This looks to serve as channel for airflow and is noteworthy because it makes the optical drive's SATA connector much more difficult to remove and quite difficult (for me anyway) to reassemble as it is a very tight fit!
In order for the logic board to come out cleanly, one should remove the RAM at the end of this step.