Yea
8.0.10512.142 here
Btw I'm also using the Lumia 520
And yea gdr3 is available to anyone and everyone with a windows phone 8 device
Just create a windows phone app studio account for free with your outlook email and then download the windows phone developer preview app and sign in with the same outlook account then check the box and go In to settings and search for an update the way you normally would then wham bam thank you mamm gdr3
Sent from my Nokia Lumia 520 using Tapatalk