Roll the synchro around and you will notice slits on each end which gives you access to the snap rings that hold the collars in. Remove these and remove the collars and this will expose the rings. Once remove these, you can see the rings and get them out. They are brass and don't worry about ruining them on removal. The new ones can be pushed in with the proper size bushing driver. Or they can be tapped in with a brass drift punch. 50 to 70 years ago hardly anyone bought the whole synchro from GM. We went to the local auto parts who sold made in USA stuff at the time and bought a pair of rings. This is why there were quite a few NOS complete synchros available a few years ago. GM dealers never sold many. And the after market rings worked just fine.
