[JSeery]

Looked at the last photo again, you are moving the spring in the wrong direction!! It comes down from the top and the retainer with the tab with the hole in it has to be pulled out. I can't tell from the photos which valves you have, but the only real difference is straight on the stems vs tulip shaped and split vs solid guides. I would guess late model valves (straight with solid guides) but it's only a guess.

Edit: VanPelt says you can remove the retainer from the valve stem and take the valves out through the top, I have never done it that way. I now see that is what you were attempting to do. Looking again, you may have the tulip valves. VanPelt has a procedure for that spelled out also. In last photo did you attempts to pry the part up with a screwdriver that is sticking out below the retainer? It is either the sleeve that the keepers are in or the tulip end of a valve. Should be able to figure that much out fairly easily. If it is the sleeve the keepers should fall out if you pry it up (look at the figure for 51-53 valves).