Then he gets to use either mod, imo. There will be those that disagree, meaning this might need to become a separate thread. Here's my rationale:
The vision magnification is in the eye, magnifying anything the eye sees. The range finder is in the scope, which targets what the scope "sees." These can be two different things, or the same thing, but what is important is that they are separate. Generally speaking, I don't let my players with vision magnification in their eyes use many modifications in their scopes to help, because the scope acts as a sort of stopping point for the vision magnification. You're basically just zooming in on the scope. The exception to this is if your optic isn't a magnification optic.
As I said, I'm certain that there are people who would disagree with me, and they might be right - it's a topic that isn't really discussed in the book. I'm simply working off my own experience in putting magnification screens into firearm optics for the purposes of military training. What I found was that when you have the scope, and you have the target, the scope supercedes your natural vision - putting any kind of display in there presents a problem, and trying to imagine putting a scope on top of a scope, which I've done, makes it extremely difficult to calibrate and configure.
However, the rules state nothing at all prohibiting this kind of thing, so if it's easier to just stack the effects, then go for it. What matters in this game isn't realism - it's fun.