Considering that even the hybrid cars made by car manufacturers themselves are heavier than their ICE counterparts, I don't think that by retrofitting an older car you'll get a better result.
For example, 2024 Hyundai Tucson curb weights:
Heaviest ICE: 3663 lbs
Lightest hybrid: 3692 lbs
Lightest plugin hybrid: 4115 lbs
Don't forget audio quality drop when switching from audio only to audio + microphone. Shit drives me up the wall.