Yes the stopped should be made of cork. Earlier version had a driven cork with the ceramic topped cork stopper hanging at the side.
It is not from Tullamore as it has the
Tullamore Dew Company Dublin Ireland I believe earlier crocks which had been bottled from the original stocks of Tullamore from the 50's and was used up to probably mid 60's would have been bottled under either
D.E.Williams LTD & later
Tullamore Dew Co Ltd i.e. without the Dublin association to the company name, I believe this is the case but can be corrected on that.
However as this is a European bottling there are 2 big clues on the bottle.
The 40% gives the clue that it is post Janurary 1980 due to the EU standardising the % from
over proof to
ABV in Janurary 1980.
However it was not till Janurary 1990 that they standardised spirit bottles to 70cl.
So your bottle is between 1980-1990. Sorry I can't be any more accurate