I feel your pain….night before the hunt throwing everything together. It’s a staple of my routine! I don’t like mounting a GoPro to my gun because as you said, you miss a lot of the action of the bird coming in, and when you shoot it shakes the GoPro so much you miss a lot of the action. The head mount is really easy especially if you are running and gunning but you have to be conscious of not moving your head a lot otherwise you’ll make people sick when they watch it! 
Now some other options which have yielded some terrific turkey footage in the past.
If you use a decoy place your GoPro 5 yards behind the decoy pointing back towards you, it’s a really cool angle but if the bird doesn’t decoy perfectly then you will miss it. Another one is mounting it on a stake and setting it up directly behind you. This will provide a really stable shot and still catch all of the action.
What GoPro do you have? I always run a go pro in the Narrow setting because otherwise it is so wide it really distorts objects around the outside, and you’ll end up with a crazy round world look. Also it allows for you to make the bird look larger, because using wide angle will make it look like an ant unless it’s less than 5 yards away.
If you would mount the GoPro behind the Turkey I would suggest using medium or wide to get as much of the action as possible. It’s a pretty cool look to run your GoPro in 1080-60fps. It will give it an awesome slow motion shot!
In terms of camo, all I do is tape up the blinking red light. If I am really concerned Ill pick up some gun tape and tape up the actual camera, the case doesn’t seem to matter. Hopefully by the time they would see the GoPro, it would be too late!! Good luck! 
