The file below is a scan of some letters is from Parnes L’ Dorot, a collection of letters written to R’ Eliezer L. Prins (See Introduction to PL and his entry in NEJ for biographical information). There are letters from virtually evry scholar/rabbi of any importance of the 19th- earlier 20th century and anyone interested in that period must make sure to get a copy.
I have left out the first letter from his father since it didn't contain anything of importance. All of the necessary background information is contained within the letters (supplied by the invaluable notes of Dr. Meir Hershkowitz and Neriah Gutel). The discrepancy in the handwriting mentioned in the intro to the last letter (written when Ginzberg was 17) is not significant. I would imagine that after recovering from the flu (as mentioned in the letter) Ginzberg was still to weak to write so he must have dictated the letter to someone else. I must say that the almost condescending tone that Ginzberg uses when writing about the Mateh Levi is certainly not worthy of him. (Some would no doubt say that from the lack of humility displayed in the letter one can see the character trait that lead to his later unorthodox career.)
In any event, the chiddushim are indeed impressive for a boy of his age (allowing for the fact that his father may have helped him) and one can understand his father’s chagrin that his son had become a “mere” scholar rather then the Gaon he could have been.
I uploaded the file here: http://www.upfree.net/2701040
 I thank Mrs. Elsa Bendheim, granddaughter of R’ Prins and publisher of the book, who made available to my father (and hence to me) a copy of the book gratis. Also, recommended is the second volume, Parnes L’Dorot containing all the chiddushim of R’ Prins. There is also a 3rd volume of his Dutch letters.
 Even so Ginzberg never wavered in his belief in the primacy of Halacha. See the introduction to גנזי שכטר and somewhat less clearly the Introduction to Geonica (at Google Books).