The tank & seat are from a Duke II. I had to cut a fair amount out of the seat base at the back to make it fit.
To secure it I welded an M6 nut onto a steel plate & riveted it to the underside of the seat. I put epoxy in with the rivets to strengthen the fit. I then used a long (75mm) 6mm bolt to hold the seat in place. I used 6 rivets.
The bolt goes in from under the rear fender, where there's a hole in the sub-frame. The other thing I like about the big tank is that it protects the radiators when one falls.
The beauty of this is that I can change it back to standard, no problem.
Here's some more recent photos. Excuse the dirt, but that's what these bikes love!!
Pic 1 - Side view, bike currently.
Pic 2 - Front view
Pic 3 - Dash. The toggle switch is the fan override. These mirrors work well for me, as I ride with my elbows up.
Pic 4 - The bolt head at the tip of the screw driver is the one that holds the seat on.