Senior Kangaroo 2023 Q20

Each cell in this cross-number can be filled with a non-zero digit so that all of the conditions in the clues are satisfied.

The digits used are not necessarily distinct.

ACROSS

1. Four less than a factor of $105$.
2. One more than a palindrome.
3. The square-root of the answer to this Kangaroo question.

DOWN

1. Two less than a square.
2. Four hundred less than a cube.
3. Six less than the sum of the answers to two of the other clues.

What is the square of the answer to $5$ ACROSS?