For ARES mount, I didn't try it. Too much work. I saw a Japanese tried on Asahi FNC:
http://blogs.yahoo.co.jp/fumi_bnr32/61434783.html
Front and rear ends need to be re-shaped. the QD roller as well, otherwise it would interfere the dust cover moving up. I am wondering if GG might measure the dimensions from Asahi one.
For GG AK5C, I didn't have one. Hope someone will make a GBB of it
. But the mount looks using different way from FNC:
http://cyma.militaryblog.jp/e480268.html
It looks the rear end uses the same way to insert into the rear sight. But it has two screw bases on the top of the receiver.
For Stormwerkz mount, the small piece of metal is from Marui SG552's handguard:
IMAG2197.jpg
It is the screw support inside the plastic handguard. It is pretty strong fitted. Now my GG FNC is like:
IMAG2181.jpgIMAG2182.jpgIMAG2192_1.jpgIMAG2186.jpgIMAG2191_1.jpg