Hi - I have fitted central oil tanks to my SR and RGS. The one in your link looks like a typical Dow pattern.
You might be able to get idea from my SR and RGS pictures in the "Bikes, Pictures and Members" section. The title is "Just a Quick Hello", the thread is at the bottom of page 6, dated; 04/06/2014.
For the SR central oil tank, it is of the scrambler style with a side neck filler. I made a simple platform and a strap from thin stainless steel, bolted through the platform either side.
For the RGS, again I made a simple platform. This tank has a central filling neck. It came with 4 alloy welded on female thread at the bottom and just bolt on from the bottom of the platform.
Hope this is of help. All the best to all...