greenhorn with question

I've inherited a bottle of grants 25yr old that was bottled in 1987 from my grandmother who worked for the company in 87. The bottle is acutally the head of William Grant head and its has been preserved in the actuall gift box and never been opened. Would some one have knowledge about the th value of the whisky and bottle. The bottle has not been opened and is 47 yrs old. Any info would be greatly accepted.