Just relaying information that James has clarified for me in the past:
Look to the Blue Book first, then Pharo for assistance/help/guidance.
If you copy Pharo verbatim, it *could* (but not always) lead you down a rabbit hole: You'll see they use class A and B in their implementation, so you'll then have to copy the same into Redline. Then those in turn use classes C, D, and E which need to be copied into Redline, etc...
In many cases, copying classes and hierarchies make sense because the classes are core to so many parts of the system. However the default train of thought should be to make it Blue Book compatible first and leverage Pharo when necessary, not the other way around.