I have found the same thing, I have not found two sources that say the same thing as far as what is safe. My cell phone puts out 98.2G (using a LakeShore 410 Gaussmeter).
I am trying to find a extremely simple answer to explain the difference between a DC open circuit and a closed circuit. I tried to explain it with the water theory but that didn't work so well.
Why not use the face and put a new radio behind it. It seems it would be much easier to make the buttons on the face plate operate the new radio. If he wants to preserver the original radio he is already blowing that on the FM conversion. Kinda seems like a waste of time.