I just went through the same thing with the 235 in my 61. The lifters are hydraulic, and have a square clip just inside the top that holds the cap in. They would move up and down easily, but I could not pull them out, and was afraid to tear them up by using pliers or some other makeshift method. I bought a hydraulic lifter removal tool (they called it a tappett removal tool) and it was money well spent. The head of the tool functions like a puller, expanding and grabbing the inside of the lifter where the clip sits. You then slide the rest of the tool down through where the pushrod goes and attach to the head and tighten. The tool has a sliding metal hammer which you use for vertical force to remove the lifters. They were still very hard to remove, but I would have never gotten them out without this tool. Good luck!
