I knew the bottom of the Desierto wouldn't match the new 'side fairings' which is a pity but i didn't think there'd be so much difference!
If you could 'extend' the Desierto fairing 'wings' with cut sections of your old 'badge fairings' held on the inside of the Desierto and bolted using the two stainless bolts like on the newer Desierto i think it'd look ok and you'd have to know what you were looking at to see the difference. You could use black allen bolts to join the existing Desierto wings with the extensions.
The black plastic has a very similar texture so should match up ok and I look forward to seeing the end result.
Good luck and don't rush in with the hacksaw!
13 G650GS Sertao, 11 G650GS/FL, 10 R1200GSA30 Desierto 3