Ignore the z axis, I've just been faffing (a product of impatience) and this is by no means my final design.

Cheers, if you have that spreadsheet still, id appreciate it! 'If you're drilling something the forces will change and actually get more balanced' is something I never considered. I imagine you could go on forever in the pursuit of perfection but i'm happy in the knowledge that it will probably be negligible

Cheers, Joe