Welcome to Mach and the new challenge. I would also join a site called CncZone (both are great places to share this info). They have a few builds of this machine over the years. Are you sure it is a 12v motor? Does it have pawls? I just cant imagine how it would stop. I have a 6 tool changer on a Dyna DM3000. It runs a stepper, pawls and solenoid. The only way I have run it or seen others run it is in 1 direction and then back up into the pawl. It claims it is bidirectional and I am hooking up the solenoid to be relay controlled to do just that. Then the tool change script will have to modified.
Post pictures too, we like them and it is nice to see progress when you look back at this. And to help others. Anyway, hope this helps.