Thank you for your input on the subject of the floor plate reinforcement.To be honest, I don't think it is a big deal. You can slightly manipulate these components, without any ill effects.
For example, you can have a K-Member "spring" off of a jig, after it is built. When installing said piece, you may have to manipulate (I guess you could say bend / flex) it to align perfectly, or square it up.
Going from the front mounts, all the way to the rear....should not cause much of any issue. The mounting plates on the K-Members will easily conform.
Now, if you were going to put a 1/2" or larger spacer there....I'd day, yes, space both ends.
At the end of the day, if someone does not feel comfortable with a 3/16" plate on the rear only, it would only take an hour or so to make some plates in the same thickness for the fronts.