good location for seacocks?

[adieu]

Hi, I''m reinstalling a head that the former owner removed to install a double berth. The old seacock holes were also glassed over.

I have an idea where I want to put the new holes, but would like opinions. I''ve posted pix and descriptions at http://www.adieu.nu/head.htm

Can seacocks be too far forward? Any problems I might encounter? Is it possible to determine the thickness of glass without drilling?

Any thoughts appreciated.

Jim Burgoyne, s/v Quiver, Phuket, Thailand