Buying a complete both removes that swapping of parts & is not that much more for peace of mind, but you still need the extractor parts as they dont come with it.
You will nee a .223 magazine follower also as the .223 box is shorter due to the baffle in it.
Bolt head swap parts.
Head, ejector spring, pin, ejector, extractor, extractor spring, extractor ball.
The firing pin hole may need to be drilled out also.