Thanks for the link, I had already found that site doing the same Google search. Great minds think alike. This Apollo is built in and has a light and exhaust fan underneath. The screws that hold it are accessed from the cabinet over the unit. I don't think I have the talent to make the hole bigger but installing something smaller an trimming it out is more in my comfort range.
I have learned that Sharp makes a kit to wall mount some of their counter top convection microwave units which includes constructing sheet metal ducts to exhaust heat back out to the front of the unit. So as not the trap the heat behind the unit.
I had hoped someone new of an exact fit replacement making this something easy. Since that does not appear to be the case this is going to have to wait until we get back home next month.
If my cook learns to use and likes a convection microwave, maybe she will let me take the gas stove and range out and put in a induction cook top.
2003 Dutch Star, 3126B Cat.