Because that breed is so productive, its health is less forgiving of a poor diet. I think it can be done well without commercial feed but it would take much more attention to the feed and the birds than ancient people needed to give their birds to keep them healthy.
I would start with making everything else as good as you can... lots of clean, fresh water will help them use the feed they get as well as possible. Extra space with a flock of other chickens but not crowded and with bushes or fences or tables to hide behind or under will keep the stress level down which will help with digestion. Grit and calcium (ground egg shells or oyster shells) available. Probably loose mineral salt, also... I think that is added to commercial feed.
Fermenting grain (and commercial feed, if you have some sometimes) will make it more more nutritious. So will sprouting the seeds. Insects, especially grubs, are good feed for chickens. Fresh greens are important for vitamins and minerals. Fruits and vegetables are good too. More than one kind of any of these things is better than just one.