Hi,I can answer most of your questions as I also am interested in ZG47's and own a few.
The year of manufacture is stamped next to the proofmark , 1956.These rifles were only made from 1949-1963.
The style of the stock is typical of the ZG47 but the carving in the stock is not.The Brno factory of the time had a custom shop.I could not tell if the stock was factory carved ,or if it was done at a later stage.(it might have been done by your grandfather)
Some of the stocks I have seen did not have the cheekpiece or the schnabel tip.
The barrel is also the standard type ZG47 design.The only heavy barrels I have seen on a ZG47 is on a snipers rifle , labled as the ZG47sn and on a cased target version of the ZG47.
These rifles were chambered for 6.5x57,270,7x57,7x64,30-06,8x57,8x60,8x64,9.3x62 and 10.75x68.
From the custom shop , 5.6x61 vom Hoffe and I have a 8x68s.(The only one that I know of)
There were only 20 000 of these rifles manufactured.The value would be only what a person was willing to ACTUALLY pay , but in your case mostly sentimental value wich is worth more than money.