Thank you for the guide. I found it generally spot on and was successful in swapping the HDD with a Samsung V-Nand SSD 860 EVO (2TB). I did use glass suction cups to get a good lift on the display which I think helped. With this upgrade I am betting another two years of service before I’ll feel compelled to buy another one.
Guide was spot on. As noted above, the TRIM feature associated with SSDs is not implemented automatically under iOS. Easy enough to start and recommended.
This question about thermal sensors and Late 2013 27" iMac, need or not. There still seems to me at least uncertainty if it is needed. Especially when substituting a stock HDD for a new SSD. Would the authors and iFixit maybe add their position on this question?