Zukes Power Bones have quite a few ingredients. If you're concerned about possible food issues, stick to the beef and rice. For a treat, give him more beef--it tastes different from your hand. Honest.
Also, just a note: while he may never have received beef from you, he may have had it in the past, so may not be novel.
ETA: I haven't read all the posts, and I'm not sure what all has happened. However, here at GI Troubles R Us, we've had a lot of bloody poop, and your plan is quite similar to what my vet always suggests: one type of food, tylocine, sometimes flagyl, and sometimes misoprostal (an alternative to carafate).