Looks like you need a couple of these:
https://socalautoparts.com/pro...p-stop-rear-stock-2/
I think that should fit the mushroom on the “good” side if I picked the right one.
For the other side, the one that the mushroom rusted off of, you have several options and remember that the only force that snubber will ever see is compression from the top.
OK, so given that the compression force will never pull the snubber away from the seat, I would clean up the seat really well; wire brush tip on a drill, whatever it takes, just clean the heck out of it. Maybe even use some rust preventative on it. Then, go to NAPA and get a tube of 3M weatherstrip adhesive and use it to goop up the seat and just stick the snubber right onto the seat (watch out for adhesive coming out the bottom). Let it set up for a couple of days and I bet you’ll have to use dynamite to remove it.
Maybe @Alan Merklin has some ideas, too.
BTW, I never installed the rear snubbers on my IRS car and even though it’s lowered (a lot), the suspension never compresses enough for anything to hit.