That’s the right idea–My mother in law (original owner of the piano) said “They’re upright when they’re vertical, but when they’re horizontal they’re grand.” Pretty cool how I put that built-in BUMP bonus question eh? Right then.
It won’t permenantly damage anything (assuming it is moved correctly). However, you’ll need to get it tuned after you move it, and probably again within a year as the piano adjusts to the changes in temperature and humidity.
It wouldn’t hurt to allow time for the piano to adjust to its new environment before tuning. I bought my first a few months ago and was finally able to retrieve my grand from my mother’s house. Her house is only two years old, whereas my house is more than 70 years old. It was suggested that I allow the piano a few days to get used to the difference in temperature and humidity before having it tuned.
The reason for waiting is that the piano will stay in tune longer if it is given time to adjust. However, given that it is 40 years old, you’ll have much less a problem with that than someone with a new piano. New pianos need frequent tunings.
Keep it in a moderate part of your new home (not in the sun or beside the air conditioner) in a relative humidity between 45% to 65% – you will probably require a humidifier in Denver. Give it some time to adjust to its new home before tuning, voicing and regulating.