David,
welcome to the forum. You can see a few examples of the various Hanover Horse and scroll if you look in my West Yorks album
http://www.britishbadgeforum.com/for...hp?albumid=175
I think all your questions have been responded to which i would agree with. I think you may have been given a bum steer by the museum. Many of the `staff` are actually unpaid volunteers helping out their old regiments. The Museum also contains the 4/7th Dragoon Guards so the person you asked may not have been familiar with the badge construction. As stated before it is a common officers undress cap badge. With the detail to the back i would suspect it was made very late in the regiments career, if you look at my album the similar officers badges i have illustrated are Victorian / Edwardian with a much different back. The reason the components were riveted rather than braized i would suspect it to avoid damaging the silver and gilt plating which do not react well to the extreme heat of braizing.