Hello, I don't have experience upgrading iMacs, but I did about 15-20 minutes of research and this is what I found: It's (fairly) common to upgrade to a 3.5inch hard drive and the Toshiba you were looking at should work, but on the topic of fan issues according to a couple of questionable sources the new hard drive could have bigger heat outputs I don't know how much this would affect the Mac. I hope this help and if I find anymore information I will let you know.
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