Overtaking mirrors for 401.

[Geoff Kingston]

I want to fit a pair of overtaking/rear view mirrors on my 401, I don't want to make holes in the body work so am thing about the type that clamp to the door window channel as advertised by companies like Holdens. I am probably being thick but from the pictures in their catalogue it is not clear to me how they clamp to the frame, am I correct in assuming they fit partly into it with part of the mount against the class and tightened up on the outside of the frame.
That being the case are they a good fit and stable in use are there any that owners have found better than others and are there any to be avoided. I have seen some of the small rectangular ones that seem to be quite close to the side window glass are these any good, do they give a reasonable view for reversing or should I go for one of the larger round mirrors. Any advice much appreciated.
Geoff.