Cutout Placement help

Working on a 66 Dart with a 408. I have TTI headers and also bought their x-pipe as well. I am wanting to add cutouts into the X-pipe before I permanently put in place. My question is how do I know where would be the most effective place to weld them into place. Also do they need to point down or can they be mounted towards the sides? I am just going to be using manual style since I will only open them during a race day. (or maybe if the neighbor pisses me off!)
Thanks for any help you can throw my way.
Rod
I hung mine down but I see no reason why they can't go horizontal. Just mount them after the X pipe