Old Unmarked Bottle of JW Extra Special

[NJJohnnieFan]

I was just given an old bottle of JW Extra Special. The only label on the bottle is a gold diamond shape that says: "distilled and bottled in Scotland under British Government Supervision". The cap is gold with black lettering. It says on the top Extra Special, the side of the cap says Built in Pourer and John Walker & Sons Limited.

It is a very large bottle 13.5 inches tall and 3.75 inches across. The bottle is mounted inside a black wood and metal tilt pourer. The bottom of the bottle says "liquor bottle" the code Z 960, the word Scotland and a symbol with the letters UG.

Any thoughts to how old this is or if it's still drinkable. There is some sediment, but otherwise looks good.

Thanks for any info you can provide.

NJJohnnieFan