Alain,
It is SN 136; the magazine is SN 143. Suffice it to say, I would be willing to pay some very serious money for an imperial Navy magazine with that SN!
I am not certain about the toggle checkering, but if I remember correctly that was part of the transition from the 1903 Prototype test pieces to the production 04 guns.
Tom A. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />