FWIW, Mark, I managed to mount our Fox 2 radar detector ABOVE the right side of the inside rear view mirror and just below the roof, on the detector's stock bracket (with suction cups removed) that's simply slid under the stock Pantera windsheld trim piece. A small piece of foam tape on the mirror takes care of vibrations from the cantilevered mounting. To get rid of the danging power cord, I hard-wired the cord to a fuse in the fuse box and ran the wire up under the windshield trim piece. In a 1000-mile test run a couple of years ago from Reno to 'Vegas, it worked just fine. This is about as high up as a detector can be mounted in a Pantera and still be inside the car, and it seems to have increased the detector's range a bit as well!
No Court of law could possibly claim that with this mounting, "the driver's field of vision of oncoming traffic is negatively impacted" safety-wise, unless its for speed-trap airplanes or a traffic helicopter! Your Valentine may be too bulky to fit up there without modifying the stock mirror mount.