I rebuilt a 4L60E for the first time 2 years ago. I bought the best parts but got stingy on tools. I wasn't confident this job was within my abilities and I didn't want a bunch of dough tied up in specialty tools if it went south.
They make a specific spring compressor. It was more than I was willing to pay. So I made this out of scraps and it worked great.
I didn't buy that teflon ring tool either. I took a set of rings to a shop and handed the tech $20 to put them on, he just ran them in dry. One had the smallest impefection afterwards so I replaced them all. I wasn't chancing someone else's work making this fail.
To avoid the tool I cut a couple solo cups into sheets, wrapped them around the shaft, put the lubed up teflon ring over the cup, moved it into place and dropped it in the groove. Then I wrapped the solo cup sheet around the outside and put a hose clamp on to shrink the teflon. I didn't take pics, wish I did now. two years later and this transmission is still awesome. I liked building the thing too, I look forward to building another someday.