Just a small puzzle

You can get the most significant digit (the leftmost) of a number pretty quickly this way

(define (leftmost-digit base n)
  (if (< n base)
      n
      (let ((leftmost-pair (leftmost-digit (* base base) n)))
        (if (< leftmost-pair base)
            leftmost-pair
            (quotient leftmost-pair base)))))

The puzzle is to adapt this code to return the position of the leftmost digit.

(leftmost-digit+ 10 46729885)  would return two values, 4 and 7