To compress the low reverse spring in the rear of the trans housing
images (3).jpeg

images (4).jpeg

Need to compress it to get the snap ring out.
Looks like the commercially available ones lock inside the castings in the trans body and push it down. Which is kinda odd because then you have even less room to get your snap ring pliars in there, and if you are this deep in the trans the shaft comes out anyway. I'm sure there's a reason.

Should work on most GM autos too, not that I expect to rebuild any more