Wow...I don't want to say the wrong thing and have you ruin your dad's Nova.

I can only say that I used a few different things on my E30 M3 when I clayed it and it had a paint job similar to the one you are desciribing, it was $13,000 paint job. I tested what worked on a part of the car rarely seen (under the wing) and actually found that a brand new 3M fine grade bar along with Mothers spray detailer let no scratches, no traces, no nothing but I was very careful to use light pressure and slow motions.

I can promise you that everyone else that will post in this thread will give you a different opinion, and they may be right, but you will never know until you start trying something. Each car/paint is different and responds differently to products accordingly.

Good luck...and go slap your brother for me.