I might be wrong, but I'm pretty sure Brian Nelson did a lot of the Ironjaws as well.
You are right! The Ironjawz Megaboss is 100% made by Nelson (and you can see it, it's amazing, face and everything), there is also an interview about this in the white dwarf at the release time of them if i remeber correctly.
That said, the "old" nelson ork head are for me the best, the gorkamorka bosses above all! But these last seen, buggies one and wartrike bozz ( ), are not so bad,,, anyway i must admite that i found annoying that every new kit or ork release the face of our beloved greenskins change a bit! Not a big problem, not at all, they are not real changes, but it's like there is always the fear to look at these news faces hoping you will like them