I dismantled two engines, both being '49-'53. The valves moved
in the guides, not easily, but they were not locked solid. I was able to pry up the spring and retainer, remove the locks, and once the valve head was pried up clear of the seat, the valves could be worked out. Twisting and using a rust penetrant helped.
With the valves out it was then a matter of using a short section of pipe as a punch to knock the guide down far enough to remove the clip. The pipe being softer than the guide didn't do any damage. With the clip out, to remove the guide I had to use a homemade puller arrangement with a plate resting on the top of the block, and a bolt going through the guide with a heavy washer and a nut. I welded a bolt small enough to pass through the guide to a larger bolt to use as a puller.