54. In the case provided for in section 53, the assessor who is preparing the roll of that other municipal corporation shall, where necessary, furnish to the assessor who needs it, on demand, the information necessary to establish the average rate of the neighbouring unit. The values thus furnished must be adjusted to the same proportion of their actual value as the other values entered on the roll of the municipal corporation in the territory of which all the land contemplated in section 47 is situated.