While I don't have printed resources in front of me at the moment, I'll go on record by saying I believe power windows were standard on Miller-Meteor professional cars, beginning in 1975. The reason I state this is twofold: Off the top of my head, every '75 M-M Cadillac ambulance I can think of, including the two parked in our garage, has power windows. Second, I recall the options being a bit odd when it came to the Criterions:
In 1974, the Criterion came with standard power driver's bucket seat, but manual windows. In 1975 and 1976, you got power windows, but a manual driver's bucket seat, due to the swivel feature. (The front bucket seats in a 1974 Criterion are different than those of a 1975 or '76 model.)
As for the brown dash, I've seen several in 1974-76 Miller-Meteor ambulances. In fact, a 1976 Lifeliner, bought new by Carteret, NJ First Aid Squad has a brown dash, despite the rest of the interior being blue. My favorites, though, were a pair of '74 Lifeliners ordered new by Murphy Ambulance Service in St. Cloud, MN. Both were equipped with red dashes (even though the exteriors were orange and white!)