Allen, Here's what I would do, get a piece of 10 Ga. plate(1/8") big enough to allow you to make a mounting hole in the front and the rear of the grinder similar to what you show on the sides. (think copy the base and turn it 90º), Then drill the new plate and the base with a pilot hole that will allow you to Tap threads into the grinder base, closer to the center of the grinder, inside of the original mounting holes, then countersink the bottom of the plate and attach the new plate with flat head screws up through the existing base. This will raise the grinder slightly, but I don't think it will be enough to cause a problem. Then you could mount the grinder with the holes in the new base plate.
Probably not a clear explanation of what I am trying to say.
I'm supposed to respect my elders, but its getting harder and harder for me to find one now.