Well, for the most part, the Word Bearers, to this day, do tend to show more loyalty to their Chapter than to their Legion as a whole, so really, what you need to do is either look into the diffrent chapters the Word Bearers were seperated into, or create your own and use your own iconography. A cross? I dont know. I dont really know if anybody was using any cross incons during the Great Crusade, but I suppose you could. But you'd have to remember that there are a good number of
BT players out there, and if you want to show this army off to people, you're really gonna want to add some flaming book Icons to clearly show that they are Word Bearers, pre-heresy.
Id advise just scraping off the crosses, and putting some small books at the end of the chains on the
BT bits to make it look like they are covered in books and scripture, since thats usually how they are protrayed. I think there are a few of the Horus Heresy series books that either focus, or mention the Word Bearers, you might ask in the part of the forum dedicated to the discussion of lore about some of the things the Pre-heresy Word Bearers did for armour and such, theres bound to be a few with special knowledge of that area. Hope that helps!