What could be helpfull.
We should keep in mind what we have as a common heritage every Christian can refer to.
These are for example besides Holy Scripture the seven oecumenical counsels.
To be reread here.
http://www.intratext.com/X/ENG0835.HTMWhat is often forgotten: the conservative Protestantisme including Anglicanisme widely agrees with them. Scripture holding supreme authority does not mean that all dogmatic belief is refused.Disagreements might be found especially regarding the seventh council mostly from the calvinistic side, but Highchurch- Anglicanisme reapproached lutheran and catholic views.
So it is not at all surprising that many aspects in Chesterton and Lewis writings are in harmony with Catholicisme and Orthodoxy.
Regarding Lewis words in Mere christianity he simply states the protestant view of ecclesia invisibils.
If we want to sort out what is specifically catholoc/orthodox/protestant in the writings of Chesterton and Lewis we have to to look for statements that can refer only to one of the different Churches confessions.
Lewis clearly speaks of a protestant view of Chirch when he says that god will sort it out, although he might be in harmony with Catholicisme and Orthodxy in many other aspects.
Now what about Chesterton? He clearly is not tending to protestantisme, also many of his sayings are in harmony with old lutheran teaching. His negative notions tend more to specific forms of calvinistic teaching.
What in his work can only and really only be accepted by Catholic or Orthodox creed?
Differences clearly- the filioque in the Creed as necessary ( originally totally un-catholic and a German Sin
) or totally to be refused, the differences in the definition of original sin and justification,papal infallibilty and so on.
If he clearly takes sides in such question beyond debate he can be located without a doubt.
Now he was doubtless Catholic and Orthodoxy was simply far away and maybe not so much in his focus.
Please note - I did not post these things to start a discussio what we might believe to be true- that is absolutly of no consequence regarding the topic.
Iustitia est ad alterum.