Tool Changer DIY with a Stepper or a Servo?

Hello,
have mesa 7i97 running and use 3 axis with AC Servos. So i have two axis i can use in future and so my idea is to use one of them for the Tool-Changer Carousell i build by myself.
The question is - which system of motor and drive is good enough  - so a closed loop stepper is okay - but how can i wire a stepper to a 7i97 or for the easiest way should i use a servo - so i can connect like my other axis on the 7i97?
The prices around 200 € for an simple ac-servo and around 100€ for an closed loop stepper - i need only a small one i think - it rotate only 8 tools. My Tools are special on SKI 20 not SK20 - that made the tool-holder very expensive. Around 600 € for one. So i don't think i will upgrade to more as 8 tools - now i have 5 holders... ibag HF80 SKI20 spindle expensive one for 40.000 RPMs.
Have someone build such thing and have any ideas?
I want to build something like this:

oh..wrong category - can a mod move it?

Hmmm.. i thought there was an category for machine hardware and wiring... or similar... but now - nothing... If i ready with my machine who can i present my hal and ini and so on... for others they also want to use linuxcnc on mesa and yaskawa ac-servos etc..?

So i think Hardware & Machines is good for this topic.

The ATC itself have no sensors - the VFD have some - like Temeprature, RPM, Failure of Spindle etc.- but for Clamping and Unclamping it looks there is no sensor inside the IBAG HF80. My idea is to build an sensor under the ATC - a very small one to check tool is inside. I mean the ATC is working over years without these sensors - but for me it looks better to control this - i have seen tools learn flying after a tool-changer problem because of alumnium-chips - and the spindle was damaged on the top - very expensive for the friend of me. Was Portatec wth an 12KW Spindle.