So here's your problem with using speed instead of range for the grab, you'd need a medium or large base to represent the rancor, right? The movement tool doesn't fit the outside circumference; that's part of the function of the notch. Better to just stick with range 1.

I think the rankor would be better as white defence, but much higher health. A creature that only has skin as a defence doesn't sit well thematically with a red save and armor.