Hi
First, you should be sure that your camera top/base plates are brass and not zinc.
the change was made mid-M4P production.
Assuming the camera is chrome, you need to find a plater who does a electro-plating of nickel-chrome, and remove the plating.
Then the trouble begins: Brass is a very difficult metal to paint. I tried to do it myself, and the result was not bad looking at all, but paint flakes were quikly falling from the camera.
I ended by sending the plates to Robert Jagitsh and he did a beautifull job, and it seems durable.
No brassing/paint flaking at all (admitidely, I take care of my camera, but in similar conditions, my amateur job was quickly falling apart). Robert is also a great guy to deal with. I would recoment you to send him a mail and check with him...
good luck