I'm wondering if anyone has info on whether a Biltwel gravity furnace has asbestos inside?

If it is a real old model it is possible that the refactory used in the combustion chamber has asbestos in it. Most of it will be incapsulated but when you tear it apart to dispose of it the dust will fly. Most gravity units from years ago also had asbestos wrap on the large gravity supply pipes. These can also be of a danger when removing to replace the old unit with a new unit.

Many years ago HVAC companys would remove the old units but since all the noise about asbestos they now hire an asbestos abatement company to get rid of the asbestos.