When you put the two side by side you can see a big difference. The ngp is smaller then the ngpc. I think the buttons might be a little smaller on the ngp as well. It seems that a slime line would fit in the ngp no problem though. If you were to move the guts from one into the other I do not think the pcb would fit into it, but your the ngpc master...so you might be able to do it.
If you can then let me know...I have a silver one that I would love to transplant a color pcb into.
If you need pics of the two systems side by side let me know and I can snap some later.
-DZ