This is in the UK but I assume there is a version wherever you are! In the end I got my dealer to fit them for me - they fit perfectly and the dealer actually assumed they were Wunderlichs . The mirrors do indeed come off and form one of the mounting points. There are four screrws and some clips to remove to take off the top fairing cover to get at the other two screw positions, and that's it. Very impressed and super protection from the weather.
@OldDog :
1) In the USA's Amazon site, these appear to be the same product (although more expensive, given the appropriate monetary conversion):
Well, the UK brand is listed as VERDDE, while the US brand is listed as SAGHOM, but the same pictures appear to be used.
BTW, I just pretended to buy these (stopping just sort of the final click or two) from the UK site, here in the USA, and even with shipping added it appears to be cheaper from the UK than from the USA (with free shipping as a Prime member):
That works out to a total of USD 71.71, according to Google.
2) If you have time to post some pics, from assorted angles, of the guards actually installed on your C 400 GT, I'd appreciate it (and I imagine other folks would, too).
Note that this site has an unusually small image file-size limitation of about 1MB. If you're not familiar with reducing photo sizes (or posting them), feel free to start a conversation with me, and I'll give you my email address. You could then email the pics to me, and I'll be glad to resize and post them (as I'm comfortable doing that sort of thing, have a lot of photo-related software, etc.).