I replaced my leaky Lokar flex dipstick with a Hughes locking version from Summit. I had to cut it way down to fit my firewall recess. What I did was measure the pan end projection, then cut the upper ends, which can be done on these, so as to maintain the cross hatches measuring lines, reassembled then refilled to the line.

As far as the correct amount - a C6 is like a C4, lots of different "opinions" including Ford's own shop manuals and in different places in the same set of books