i2i beat with the basic ratchet and pawl system.
Lots of the smaller CNC lathes with basic tool changers use a ratchet and pawl, with the turret driven by a stepper motor. To change position it turns the turret for a pre-programmed amount of time (I don't think the basic ones use any kind of detent/position detection), then reverses the stepper motor and relies on the motor stalling once the ratchet and pawl lock.

It's a pretty crude system, but effective. The biggest downside is you can only change tools in the one direction, and they are relatively slow to rotate. Iknow there's at least one video on youtube of a Conect lathe with a tool changer operating.

Personally, if you're going the length of designing and building your own turret, I'd design in a stepper motor/drive system. All it would take to operate is one extra stepper drive, and a little bit programming.