This is the ubiquitous "pickle fork" flathead valve tool. It is used mostly to put the valve assembly back together since most valve assemblies I have run into are stuck to the block too tightly to move with this tool. However, it is handy for one phase of disassembly.
You will probably find that the valve locks are pretty well stuck to the spring retainers. It will make life easier if they are freed up before using a modern spring compressor to remove the valve locks. Just insert the tool under the spring retainers.
Then pry up. Unless the valve is frozen in the guide, the valve usually lifts instead of the desired action of the locks breaking loose from the spring retainers. Just tap the valve head with a hammer while lifting up on the tool and it usually breaks free. Note that these are the '52-'53 two piece spring retainers. Most hot rodders prefer to replace these with '49-'51 retainers and matching after market springs.
Pry up the valve and remove it, then pry the spring and spring retainers out with a big screwdriver. Finally, drive the guide down from the top using a deep socket of the right size or a half inch extension so you don't mangle the hole in the guide or the block. Sticking out of the top of the spring on the left is a tab with a hole in it. This is part of one of the "C clip" valve guide retainers. More about that later.
That's it for now since this is as far as I've gotten to date and I'm out of pictures. I'll update with the rest of the process in the future.