There are two things not mentioned in this guide (which is, all-in-all very good)
1. There is a short lead connected through the EMI shielding at the top of the IMac to th right (inside vie) of the camera board, to a very small daughter card marked Apple 820 2009-A 2006 srewed to the inside upper ABS case surface by a single 1mm torx screw. The lead s othere end goes to the power board. Check this has not been severed. I extended mine.
2. The Super drive DVD drive is very difficult to re-position because apart from the mounting frame ears mentioned, there are two "dowels" moulded into the ABS bezel. If these are not correctly aligned when fitting, then the CD/DVD will not eject because of the mis-alinement. The ears can be difficult to release because the unit is forced against the logic board at the point where the board to drive connector is situated.