Speedometer

Probably the cheapest way is to get your speedometer rebuilt and then get the right speedo gear that goes in the transmission. The gear would depend on your rear end ratio and tire diameter. Somebody can figure out how to calculate that.

There is nice digital way but it doesn't fit your "nothin fancy" requirement. Get your speedometer rebuilt to go with a Global Positioning System. This can make your speedometer and odometer look very original. The speedometer uses the original face and needle and the odometer is replaced by a small digital display. Unfortunately, I think the whole setup runs about $500 - $600. You could contact Redline Gauge to get more (accurate) info either way you decide to go.