I have a small warband of Fallen.
I decided to steer away from too much Chaos accessories, with the exception on my champions.
Swapping to Chaos bolters isn't a bad place to start.
One conversion I did was to modify the Power Packs so they were more like Cyphers:
It uses the large Dark Angels icon from the Ravenwing sprue, removing the sword, and replacing the exhausts of the Power Pack. I find it differentiates the Fallen from both the Loyalists and the Heretics.
Other conversion suggestions I'd give is to look up the older version of the Red Corsairs, which were basically just loyalist marines with a few Chaos bitz.
If a piece has too much Chaos Iconography just trim it off, but be careful, both to avoid cutting yourself, and to avoid removing detail you may want to keep.
Strange as it may sound, some suitable modified Space Wolf bits work to further the suggeston of not being Loyalist but also not Chaos.
Also, don't be afraid to bash the bitz box. You get some real characters that way:
Thats all I can really think of for now. Good luck my Fallen Brother