I wonder if the car came with the performance indicator like this...a lot of 68-69 C-bodies did
and if so, perhaps back in the day, ol Jean the owner ,swapped it out for a tach he had because they are cooler to have.
If that tach has this A-body only base it is a big ticket item as it would be from 68-9 Dart and tach would be 4 wire.