Thanks Alan, Have had a close look at the images on David Silver and ordered the part. Yeah, there are two longer bolts, not both the same length, one is about 20 mm longer than the other, which go through the Police spotlight mount and hold the mirror mount in place.
Haven't yet decided what colour to do the mirror covers, doubt if I'll be able to get the exact white in a spray can, so might take them both off and spray them semi-gloss black so they look like black plastic.
Any suggestions? Does anyone know of a close match for Honda ST1100PY white? Does Honda do a touch up spray can?