DARN.... I had an old Sharp that I replaced last spring.. The touch-pad wasn't working.. It was a convection / Microwave.. We never used the convection part so we visited Walmart and bought a plain ole microwave that would fit in the hole.
I got it mounted, and then made some small mods to the trim to get it to work.. It looks original..
NOTE - If you do re-install a convection type microwave, make sure to re-use / install the ducting..
Article with photos...
Microwave Oven replacement – 1999 Southwind 35S