I don't think so the powerglides are a bit different than any of the three speed transmissions, but in most automatics reversing is accomplished by routing power in the correct sequence through the two planetary gear sets, and the ring gears are not just for that particular purpose.
If you do not want reverse you can definitely remove the ring gear and use the planetary for first and second only.
The ring gear only drops in and is not used to retain proper end play.