you probably want aldldroid, it's on the app store, it's about the only thing that's going to work with the ol' aldl bus on a modern tablet or phone

keep in mind by replacing the speedometer that you're losing the odometer too, depending on where you are and what you plan on doing with it, this could give you legal issues with insurance or inspections. if you get a jerk cop he might pull a vehicle inspection ticket on you if you get pulled over speeding and he realizes you have no working factory looking speedometer

if you wanted to, you could always just get a gps speedometer app for your phone however that's only accurate on a flat surface