One of the dudes who sculpted on the line, Scott Hensey, has this picture of an unreleased Space Slammu and a Powerarm Ripster with different colors. I was actually able to find in-hand photos of the Ripster prototype on a Facebook group.
Also there’s a video on youtube featuring three Extreme Dinosaurs prototypes (a T-Bone with a Bo-Staff, a Bullzeye with extending spikes on his wings, and a dilophosaurus character that was never released):
https://youtu.be/p_rLLDB8Ga0 