What optic mounting plate do you have for your P320? Different red dots have different footprints.
I have a Holosun HS507c that I'll be putting on a Walther PDP.
I have the Sig RXP Slide on my P226 - It's milled for a Sig Romeo 1 Pro and has the suppressor height sights. This way the red dot is basically cowitnessed to the sights. With standard height sights, you may or may not be able to see through the optic window to see the dot.
You should be able to install the sight yourself, however you will also have to sight it in yourself as well.