I'm not aware of any mods to the frame rails with the HDK unless you are referring to the three small holes that you drill on each side for the shock support brace. Baby stuff.
I could have sworn I seen that the front frame rail was sectioned for the the k-frame. If not, then I stand corrected. I looked at so many different things when I was researching the front end, I could have easily confused it with something different I saw. Did n't mean to offend HemiDenny. I really enjoy looking at his work. I only wish I could afford his front and rear kits, they look great when finished.