The Kenwood KFC-4675C speakers sound like a solid choice, especially with the built-in midrange and high-range components. Using a passive crossover along with an original Blaupunkt tuner and an '80s power amp sounds like a smart way to maintain the authenticity of a car restoration while maintaining the desired sound quality.
Installing sound deadening materials throughout the vehicle was a smart move to reduce noise and improve the overall driving experience. And I must say, your son’s idea of installing a subwoofer on the center console is quite brilliant! This is a creative solution that preserves the original appearance of the car and gives the audio system additional expressiveness.
I would also recommend that you create personal software for high-quality stereo system setup. The professionals of the
https://www.cogniteq.com/ team can help with this; they will do everything in the best possible way.