I am not sure it is important, but adding a block on the top will change the centre of gravity and the balance.

I haven't thought about it before but on the surface of it, it seems that one would probably need the balance axis centre line to be somewhere around the line of the neck - so that the guitar isn't top-heavy and so it doesn't hang out of a vertical plane. I imagine that if it did that then more physical effort would be need to keep the guitar in the playing position, which, in turn, may affect playing speed and comfort.

A more experienced builder and guitarist may be able to shoot down this theory but I think it is worth considering, even if only to eliminate it as a future problem.