I think the 2 big cupped washers are to buffer the rubber bushing in the strut top mount and doesn't have anything to do with the bumpstop, without the bottom one you will drive the rubber strut top bushing down onto the strut shaft and bottom the strut top nut on the end of the threads. Unless the PSS9 rear mount has something at the top to prevent this
I have never seen the top of one in person so I don't know
PSS9 is supposed to be a really great upgrade, I bet you will really like it!