I either didn't hit submit or my posts dissapeared. BUT
Windows down is a rule so they can get to you if there is an incident. "Real" race cars use window nets. In drag racing the biggest chance for a failure and then flying parts is at the launch when you are side by side. I assume the glass will deflect or and least slow down the projectile???
I run the stock seat and belt right now with a heavy left foot on the dead pedal. I will not run a harness without a rollbar but that is just from seeing too many on track incidents. A good seat will work just as well as harness in a street car application.