John, it is a good idea to order an extra mounting plate with the large sized hole for your table. This is not something you need to do right away. I am curious about why the locking miter joint is so important to you? There are many joints we can build that offer great strength and good looks. If it is for strength and appearance you can cut a rabbeted miter joint for the same look.
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"