Well I am rebuilding the instrument console. I am using a speedhut tach and I have 3D printed a new mounting bracket. I also found that two of the bulb housings were badly melted so I 3D printed new ones.
I am going to splice the new tach wires into the old tach plug so that it will plug into the old connection the same as the original. Red - Tach signal, Black/Yellow - Ign 12V, Black - Ground and the other two for the light.