Yeah, the gland nut was easy. It was the but at the top of the piston that holds it on the thrust bearing assembly. You need to (or are supposed to) keep the piston from spinning WITHOUT grabbing the piston with a big channel lock or vice grip. But the 27mm big nut is sunk so far down in the cup, you need a socket with hex base and also a hole large enough to slip the smaller socket down the hole to the piston. I didn't have that. But I did have a big impact wrench which spun the nut off (and also probably ruined any remaining life in the insert).
Oh, right. I too used an impact gun to get the nut off.
As to putting it back on, I cut a hole in the side of a 17mm deep socket that is large enough to allow a short allen head wrench to fit into the socket in the center of the piston rod. You can only turn the 17mm nut about 90 degrees before you need to remove the socket and reindex it, so it is slow going, but it works.