Here in the original manuscript, Oliver Cowdery appears to have started to write “and they were also distinguished for their zealousness towards God”. But after writing zealous, Oliver crossed out the ous, giving the correct zeal. There are a few examples of zealous and zeal in the text but none of zealousness.
Summary: Accept zeal, the corrected reading in 𝓞 for Alma 27:27 (“for their zeal towards God”).