Here is the video guide:

Links:
–XDA page
–Downloads

Short written guide:
-Download: I9300_x.x.zip, slim common.zip
-Enter cwm
-Full wipe
-Format /system in mounts and storage
-Flash I9300_x.x.zip
-Slim_common.zip
-Reboot

WARNING:
I had to flash away from the rom, as the battery life was shockingly bad – more so, when recharging the device, the S3 got extremely hot, and didn’t take the proper charge. I couldn’t risk having a burnt SGS3, so I flashed off it within a day of use.

Hope this helped you!
–TotallydubbedHD