Many of John Maxwell' drawings were tracings that he made off of DRGW originals at the railroad's office. Others appeared to be copies of engineering drawings that originated at the railroad. The dates on the drawings are important as are photos with accurate dates. Then there are "standard plans" and "as built" plans. Again, decent photos show what it looked like at some point.
Six different lawyers will give you nine different answers on copyright infringement. It's different up to a point if you are giving it away as opposed to selling it. There is already a lot of Maxwell stuff out there in various kit plans, etc. It's usually referenced back to Maxwell.