1965 Dodge Dart Speedometer

Thanks for all of your cometns.

The speedometer runs but does not light up at night even with a new bulb

When the GPS says I am doing 60, the speedometer says I am doing 70. the faster I go, the more it is off. If I do 40, it may only be off 5 mph

I took the car for a ride. When it was complete, the odometer said I went 62.9 miles but the GPS odometer said I went 69.9 miles

The tires are 185/70R13

So I have a mechanical speedo and a mechanical tach (aftermarket on the post). I want to integrate the tach into the speedo for a more original look

Can you do a mechanical to electric conversion??