OK, until I get Allan's camera, picture this.
Look at the pictures with the red inner fender wells. You can see the factory drain hoses coming through the cowl and stopping short at the top, where the water just drains freely inside the fender.
Now look at the middle picture of the right side of the car, which still has the inner fender wheel well panel mounted with the weatherstrip still attached. The new hose goes from the old hose, slightly down and across the inside red panel to the inner fender wheel well panel that fits at the back the wheel well, where this little drain now is located. The hose fits in a hole in the back of this rubber drain grommet and it makes a water proof sealed drain to allow the water to come out without sitting in between the fender and inside panels.
It's far enough above the tire spray pattern to avoid a direct hit, but Allan sealed it with silicone in the back and sprayed the front with undercoating, so nothing is coming in from this side.
You would have to drill three holes. Two for the mounting nibs and one for the hose. These drains have little nibs molded into them that allow them to be pushed into a hole and then they expand back out and self seal around the retaining holes, top and bottom. seal around it. I'll take the extra pack that I have apart tonight and take pictures of the parts front and back. You can see it in the picture of the package on it's side, bit it's hard to understand if you're not an old fart like me that remembers these things from the old days.
I got them at Mustangsplus.com for $5.95 per set.