The Ford Barn - Where to drill the hole for sidemount

Don Turley posted a neat way to drill the hole for the side mount bracket some time ago. It is pretty simple. I am attaching some pictures I saved from his post. If you search for Don's post, he explains it well - his post is below in blue.
Rusty Nelson (Fordbarn ID wrndln)

Sidemount locating tool for 1928 - 29:
The bottom end of the tapered hole in the sidemount arm bracket is the smaller end, approximately 3/4 inch diameter. Cut a wood dowel rod, 3/4 Inch diameter X 3-1/4 inches long. Make sure that the top end is cut square to the length of the dowel rod. Drill a 1/8" hole through the center. If you don't have a drill bit long enough, then drill in the center of each end until it meets in the middle. The metal wire rod (about 6 inches long) is sharpened on one end and must slide through the drilled hole in the dowel
rod.
While under the car with plenty of light, slip the wood dowel rod up into the bottom end of the bracket (attached to the frame) until it comes squarely in contact with the bottom side of the splash apron that is already bolted in place. With the sharp wire rod, you should be able to mark the bottom side of the splash apron in line with the center of the bracket. Remove the locator tool and then with a long center punch through the sidemount bracket, punch a dimple in the bottom side of the splash apron where you made your mark with the locator tool. You should now be able to see the dimple on the top side of the apron. Now, from the top side of the apron, drill the correct size hole in the apron for your sidemount arm grommet.
Don Turley