I have been using the RRS 97L B on my HC300 for some time mainly because I had it lying around from a previous lens. It fits pretty well but has only one attachment screw. There is a ridge at the back of the plate to help prevent forward slip and rotation and it may be possible to use more than one fixing screw to the lens. I haven't felt the need to do this yet.
Thanks, Francois and Richard. The RRS B97L was apparently designed for the V Series 350mm lens, but your experience, Richard, suggests it works fine. I did contact RRS and they had the same recommendation. They offered to ship me one to try.