That is a good idea.
However, after some thought, I think I may make and L bracket that is the width of the header opening.
This L bracket would have the bottom of the L facing towards the inside of the opening with a double faced thin strip of tape to stick the bracket to the top of the refer case.
The vertical part of the L bracket would cover about 1" of the header with two holes drilled to match what the Norcold had to fasten the L bracket to the header.
I would paint the bracket to match the color of the white oak finish. Or, I could mount the bracket to a white oak finish trim piece to make it fancy.
In any case, I think I now have the final plan to fasten the top front of the unit.
Thanks for all the tips and comments.
Surprised nobody commented on the insulation burning picture. That really confirmed to me that replacing the Norcold amonia boiler operated system was a solid safety factor decision...