Hi Mat,
Sounds like a great project, be sure to visit our projects section when it’s all together! As for the motor rotation, I would suggest with a stepper motor as it will allow you to rotate in precise angular increments. Most of the steppers motors on our website should do the job, but if you can tell us the exact weight of the clock (including EVERYTHING but the motor) we can more accurately work out what sort of motor specs you’ll need.