I have a 1981 mobile home with a beach furnace. The furnace burns stove oil. Now my oil company can no longer get the stove oil so we need to switch over to furnace oil. How do we go about doing that without ruinning our furnace?

Exactly what make and model is your furnace, and maybe the manufacturer can steer you in the right direction. Did your supplier not give you recommendations for other suppliers, or a compatible oil?

Another option is to upgrade your furnace.

As long as the furnace is a gun type, you should not have to do anything to switch fuels.