I have a longish rail made by Really Right Stuff (RRS) and these are also supplied by Kirk. All of these require an ACRA style system, so their use would require you to at least buy an adapter for your Manfroto system unless it is ACRA ready. I purchased my rail (about 5-6" long) for a different purpose. For your purpose it would center your camera/lens somewhat better over the ballhead, but I don't really see a big need to do that. I have the 70-300 VR lens. It is a good lens and I give it good use. I have not seen any kind of aftermarket collar for the lens. Note too that Nikon has just introduced the 70-200mm f/4 lens which (I believe) is longer extended than the 70-300mm - the collar for this lens is optional and some Nikonians see no need for it.