I, of course, don't know your situation, but I would recommend in principle making it even closer to the melodies of the original.

Unless it's their first exposure to chant, I think congregations can handle more than we think they can. (And if it is their first exposure, might I suggest starting with a Kyrie which you wouldn't need to slice and dice at all -- like XVI or XVIII, etc.)

After having doing those two before my arrival, our parish not-that-long-ago, made the leap to introducing Kyrie XI. The pastor (who is also a musician) and I discussed how we would introduce it. We decided to keep it six-fold, since the alternation between cantor/choir and congregation would make more sense to our congregation that way (at least for now) - and the 1970 Ordo Cantus Missae seems to say nine-fold should only be retained if it is essential to the form. (Regardless if I agree with the reasoning there, those are the "rules.")

But we also had to decide what to do about the final, extended Kyrie. In the end we decided we had already sacrificed tradition by going with six-fold, let's just teach the congregation that the final Kyrie is different. "Besides," he said, "if we don't do so now, we'll never be able to go back and change it." We printed each repetition out in the worship aid and taught it just once before Mass. They did just fine with it - and now it's what they're used to.