Nope as far as I recall the mil 3 to mil 2 figures were pop tops, the millennium 3 figure on the millennium 2 body, so while some mil 2 morphs might work below the neck you may have some problems, and the mil 2 figures didn't have morph injection,  so you would have to transfer them over manually using morph manager.  as far as materials I'm pretty sure you have to use the mil 2 textures on the body and Mil 3 on the heads.