The brand name was Tappan - the model I don't know. Normally the microwave only comes on models with the propane oven. If you have a convection microwave under your burners - congratulations, you have extra cupboard space. The downside is that you can't bake in your oven without an electrical hookup or a hefty generator. Ok, you CAN dutch oven cook over a charcoal fire outside.
If you have a conventional propane oven, something happened to the Tappan microwave. It's very small - designed for popcorn and warming water/coffee. I believe I saw it in a marine catalog somewhere.
Call the factory in the morning, they can tell you the model.
So... you found a used 27 FB. I'm impressed, very few people seem to be letting go of them.
Today is a gift, that's why they call it the present.