Hi,
I can offer you those suggestions:
I did that too in the past and this is how it was done in the first:

I've simply made some small clamps that fix the switch panel. The panel is just big enough to cover the hole in the dash rail.
Later on, I did it this way, sinking the panel into the rail:

There is a bit more work involved as you'll have to enlargen the hole in the rail and weld some brackets onto the back of the panel as well as some bolts behind the rail.
Third, you might look for the switch panel of a Mini van. This uses the same switches as yours but the panel itself is larger and can be screwed onto the rail using the existing holes. (IIRC)
The only drawback with this solution is the lack of one switch, the rear screen heater (which is obviously not used in a van) But you might consider replacing the brake fluid test switch by a simple bulb which means one switch less. (Honestly - who testes the brake fluid control light regularly anyway??)
HTH
Michael