Yes, but the number which indexes the position in PI where your book starts will probably be longer than the book itself.
I'm almost sure that if we have a "book" with N characters, in average, the number of (decimal) digits of the index of that string in pi is N * log(256) / log(10). (I'm too lazy to write the proof now, so perhaps I'm making a mistake.) This is (esencially) equivalent to that the expected position is 256^N. (But I'm taking averages willy-nilly.)
If this is correct, the position increase exponentially with the book length, but the numbers of digits in the position increase linearly.