I have never seen the real David statue, but there is a head replica at the Hungarian Academy of Applied Arts, and the Hungarian Academy of Fine Arts.
I remember, when I was a designer student, and we had to draw the head.
I think the higher parts must be bigger, if the statue is bigger than life-size, because we see it in perspective. That's why a mock-up of this statue would be very strange, almost distorted.
By the way: we have a Petőfi statue in Székesfehérvár, with also big head, and huge hands. Compared to David statue, it is even more disproportionate.
In addition he wears a white polar sweater, LOL. Most of the citizens of Székesfehérvár do not like it and feel unworthy of the great poet. I have the same opinion.