When I put OD in my 67 wagon, I mounted the OD light right above the Fan switch - just about where you find the Hazard switch in the 68+ models.

For models that have both an OD and Hazards, the "proper" spot is half way between the fan and 12-volt outlet (lighter) about 1/2" - 1" above the center line.

Chris is right though, put is wherever you can see it. When I replaced the wagon's dash, and install the OD in my 68 sedan, I mounted the light between the two switches. since all the other "stock" spots were full.

There's a reason that it can only go a few places. The dash wiring to the various switches and the large chrome face of the instrument panel keeps you from putting the light anywhere else on the right side of the steering wheel.

You could go on the left, but then your best best is to put it above the wiper switch - approx where the brake warning light goes in the later models.

Regardless if where you choose, check the area behind the the dash first!
Choose carefully and use the correct size bit. There is nothing worse than an amazon with extra empty holes in the dash.