Well, the only way to be 100% sure the organs you're feeding don't accumulate any crap in them is to raise them yourself
but that is out of the question for most of us. I try to buy meat that's hormone free and raised naturally. I actually get the chicken from one brand that has this written all over the box.
Regarding the recipe you're feeding, I have a question regarding the necks: do you add them because they are cheper, for the bone content or for the teeth excercise? If you're not using a whole chicken, it's rather hard to get the calcium to phosphorus balance right.
If it's not cost related, I'd drop the necks (you can feed them as a whole meal, once a day, 2-3 times a week). It's also better to use the same type of protein throughout the recipe.
Cats generally do not need fiber, especially if they've been eating raw from the start. The problem comes in older cats that have been fed a comercial diet. Sometimes the elasticity of the intestines is lost and they have trouble moving the bowel content. These cats can benefit from added fiber that bulks out their stool.
It's normal to have small, dry poops. If they're going regularly and not straining, it's probably normal. But if you do want to give fiber a try, give psyllium powder a try.