Here Peter - a couple pictures of the W-Wadeco Shifter reverse blockout plate assembly.
It is cleverly designed so that it is a slip fit under the shifter gate plate and is retained by the 4 allen heads (friction / compression interface).
It is a reverse "block" (you can't accidentally hit reverse going from first to second), AND it will allow you to put the car in Reverse, and then lock the shifter in that gear, so it doesn't pop out of gear and start rolling around.
It can also be quickly and easily removed for those "Concourse" events, and then installed for racing (I am using it in the first picture).
To make it, you need an aluminum hinge, a sheet metal bending brake, and a little fabrication and hand hammering for the custom curved "thumb tab".
The sad part is how the close-up pictures make a car look so crappy. My car, shifter, shift plate and my W-Wadeco lockout don't look nearly so bad to the naked eye.
Rocky