A majority of the things pictured there are generic and can be gotten rid of. The disc horn, the double-sided horns, the screws and the brass sleeves can all go away. It's just stuff that is put in with a servo so it can be used in pretty much any scenario (planes, cars, etc).

You should take the servo and horn (or the whole truck if you rather) to your local hobby shop and have them match something up for you. Just looking at the pictures, I don't think you have anything on hand that will help your situation.