John,
I would say that body fossils include the molds and casts found as fossils as well as petrified original remains. I think this works for what you are trying to understand. Technically the molds may not be body fossils since they represent the negative space left by the now missing original body material.
As far as trace fossils go, the ones found “in the wild” are preserved in different fashions that are described in Osgood 1970 and by others. Yes, you can make a mold from these originals and then make a cast from the mold to make a cast replica. I really think that is all you need to say. Simpler is better. No need for long detailed explanations.
Jack