Hi cgchris99, I use a 1" round hole for the Flash. I also use the silver metallic duct tape around a thin piece of foam to seal between the camera and the glass. Sort of end up with a silver doughnut looking thing. You can probably use any shape of hole to fit your housing and design.
Pretty sure mine is a 1 inch hole as well. I was very surprised at the range of the flash in the PF camera. I used foam rubber to block off the flash from reflecting back onto the lens opening. I was able to get a high-quality lens from a local camera shop for only five bucks to seal over opening for the camera lens. He had a box full of them that he considered almost "throw away" lenses.
Mine is around 1.25 " wide. I was using .75 because That is the hole cutter I had. The light was strong right in front but weak on the sides. The bigger hole did make a difference. I was using the OWL. I just bought two OWL PF's. Will post the difference in a few weeks. I'm sure it will be substantial.