Piston Size and Brand?

[rztoome]

I just got a hold of a used RZ motor. I pulled the head to check the condition of the top end. I haven't pulled the jugs and don't really want to (if I can avoid it). The piston has a "200" stamped on top, and no other visible markings except the forward arrow.

 

Can anyone tell me what the "200" means, and, what brand piston this might be?

 

Thanks all.

B