Everything mentioned so far sounds like agreeable guesses. My view is this gun has been re-stocked and custom engraved a long time ago, but not by Browning. The wood work and especially the checkering look very un-original in style and execution. The engraving looks good enough, but is also suspect. Just my opinion after looking at many, many Superposeds over the last 35 years.
JR

Be strong, be of good courage.
God bless America, long live the Republic.