Am I completely screwed?

[everywherevirtually]

doesn't metal and aluminium have a chemical reaction after a bit and weld together ????

Yep. It's happened on my Marin mountain bike. The alu seat post has welded to the steal frame. Luckily the seat is at the right height

 

[Moosly]

Just resurrecting this thread from the depths topoint out that the fitting kit for the Givi bars now includes the right size bolt.. All went on my 650 very easily.