TriSpec,
What led me to say the tank was "around 1957" is that when I compared the tank in the photo with two contemporary illustrations ('54 and '57) I noticed that the front mounting brackets seemed to match those of the '57 illustration, they appear wider and more rounded than the more triangular shaped brackets shown on the '54 model.
Perhaps you will know the actual year that the bracket style was changed?
Further research would seem to suggest this was after '55?