Sorry, Brian, I wasn't too clear with that info.

You pry the spring down and remove the upper retainer if you're removing the valve, spring, and guide as one unit.

All you need to do - probably - in this case is use a tool to compress the spring so you can get the keepers off and then lower the spring back down on the lifter (those two semi-circular wedges just like modern valves) This frees the valve so it can be pulled out of the guide.

Reassembly is the reverse.
Shade tree trick when you reassemble - daub some grease on the keepers before you try to stick them in place. The grease holds them on the valve stem while you carefully lower the spring/retainer back in place.