I've got a 2010 21.5 iMac. What size is your iMac? Did you remove the ODD? Did you do the work yourself? Does the iMac run the 830 at SATA III speed? Sorry for all the questions but I'm really wanting to put my older 470 SATA II ssd in the iMac but not sure I can do it myself.
I have an early 2009 20" iMac. I did remove the ODD, I did do the work myself, and no, it will run at SATA II speeds but that's fine (though not on 2011 MBP but that's another story). If you are starting from scratch, the sataIII disk can go in another computer when the imac retires.
I don't think it was that hard, I just get all my instructions and reference videos to hand, containers for each screw type to keep them straight, and have magnetic screwdrivers, a LCD cleaning kit for reassembly, and two dent-puller type suction cups to pull the glass. I also work very slowly, so as not to make mistakes, but that's my caution.
Ifixit website and videos, that and OWC in the US for parts. I'm in the UK, I use
http://thebookyard.com for the same.
Watch this super cute tech girl show how to remove the glass/lcd/hdd
http://www.youtube.com/watch?v=3w6E2_XqaBw
Here's someone doing a quick and dirty version on a 2009
http://www.youtube.com/watch?v=Lp7_AP0wc7s&feature=related
http://www.ifixit.com/Device/iMac_Intel_21.5%22_EMC_2308
Just be aware of the temperature sensors around the hard drives, and the potential issues there and have fun
Here is a tutorial on your model
https://forums.macrumors.com/threads/842548/
