not sure if i have read all the above currectly but i get the impression that you want to use your 2wd cams in a 4x4 head, (i may of got it wrong)
the 4x4 head is indeed a better revised head over the 2wd but the cams (if they are 2wd cams) will not fit into the 4x4 head as the cams in the 4x4 head are longer.