Hi Marv
There's another difference in the mesh concerning chest->collars so you cannot swap chest morphs P3 <-> P4.
i.e. the torso (rigt and left collar, chest, abdomen, hip as well as the thighs) is NOT morph compatible.
The other bodyparts should be, thou some morphs do not import directly. But you can always use MorphManager to copy them.
The main improvement from P3 to P4 was IMHO the new UV mapping with the big face.
BTW, Yamato's improved joints
http://www.posetteforever.com/viewtopic.php?f=21&t=1354 work on P3
Posette as well as they do on P4