Ouch! We lost the guides for the 27" iMac EMC 2429
Here's what I could find:
https://www.ifixit.com/Guide/iMac+Intel+...
https://www.ifixit.com/Guide/iMac+Intel+...
https://www.ifixit.com/Guide/iMac+Intel+...
https://www.ifixit.com/Guide/iMac+Intel+...
There are others which I can't find on the Web.
Is this a good question?