DVD REWRITER I have just bought.

no unfortunately not. The GA11N is a SATA drive, whereas your 2007 iMac still uses a PATA connection. (iMacs from 2009 and later use the SATA connection)

You want a 12.5mm PATA drive with a 32mm feeding depth (because of the extra depth created by the aluminium bezel)

Here are a few models that will work, but there are 2 versions of each. one has a 22mm feeding depth and the other is 32mm. It doesn't seem like a huge difference, but you will need to use something to push the disk in if you get the 22mm version, as it doesn't grab the disk until its passed the aluminium frame...

Panasonic UJ-875

Pioneer DVR-K05

Pioneer DVR-506PD

Sony AD-5630A

Sony AD-7640A

Also, you will need to check what drive you currently have fitted, as each brand of drive uses a different optical bezel that clips to the outside of the drive, so if you change manufacturer you will need to change bezels too (you can alter the bezels to make them work on different manufacturers, but its much more straight forward to replace them)