There are no stops - you need to run a rope. The SN pole mount is so flimsy that I didn't even bother putting stops on.
You should be able to run any RN spring, but I have had one complaint about the lower part pulling out of the base when the pole is all the way down. I don't have specific numbers, but I think some of spring manufacturers make the long part of the spring too short. It just comes down to trial and error. I am running a couple-year-old blowsion spring on mine.