I can't verify it yet, but I'm about to find out. B110s are still around here in Indonesia, far more than B10s, and a wrecker near Cibinong has a 1200 sedan he's breaking for parts. I asked him to keep the front rebound bumpers for me.
My plan is to put one next to my old spring support on the bench before anything goes on the car: base diameter, stud length and thread pitch with a gauge, and how hard the rubber is. If the stud is shorter it won't matter much on a bump stop but it might on a spring support, because that part takes the load all the time, not just at full compression.
I'll post photos and measurements in a week or two. If anyone has a B10 support with the original part number on it, a photo would help.