Be careful with that:
4. Wildlife Found Dead:
You may remove and dispose of wildlife found dead
on your property or an adjoining public roadway,
but you must first notify WDFW. Dead wildlife can
only be removed for disposal, not for personal use or
consumption. (WAC 232-12-287)
5. Possession of Antlers:
It is legal to possess naturally shed antlers of deer,
elk and moose.
For 5. it does not talk about antlers off of road kill. Would hate to see someone get pinged for an honest mistake.