Chris, welcome to the site!
1. The round base antenna. NOS is best, but a reproduction will work. Most suppliers carry the reproduction.
2. As previously stated. Natural paint will work, but this is a concours forum so most of your questions will be answered in that manner.
3. Scott Fuller exhaust is the best available. The cheaper reproduction exhaust will work, but may require some tweaking for the best fit. I don't think a local exhaust shop will be able to get a better factory appearing system than the currently available systems.
Danny