One of the Japanese modellers has a set of instructions, and a revised neck mesh, to put the V2 head on the V3 body. I've used it, because V2 has some head morphs which V3 doesn't. If you're doing stuff with P5+ math nodes to generate materials without texturemaps, both V4 and V3 have awkward features in the UVmapping. Some things are still easier with the V2 mapping.