There are/were two types of roof rails on E70, one of which is this same type. I had it on my X5M.
Get the OEM BMW cross rails that fit the flush rails - much easier to work with (but still a pain to install). They have a clamp that basically pulls up onto the ridge in the rail to hold everything on.
I used to have my Thule roof box on the top of the whole thing - worked fine...
