Brainteaser 1457: All square

From The Sunday Times, 12th August 1990 [link]

Your task this week is to place a non-zero digit in each of the 16 squares shown:

When you’ve finished each of the four rows should read across as a four-figure perfect square, and each of the four columns should read down as a four-figure perfect square.

What is the sum of the 16 digits?

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