PJF

Hi people i have a 97 impreza turbo and need to fit some new bump stops as both rear ones have perished, i have bought some universal powerflex ones which are a standard height.
What i was wondering is what height size should they be for my standard suspension?
I am assuming to fit them i have to take the top rubber peice off the strut and slide them down, is this correct? or could i just slit the bump stops vertically and fold them around the strut/piston (sorry not quite sure what the correct term for it is)
any help would be great thanks