There are tools you can buy which have been designed to take out and put back the valve springs and keepers.
I think it was about $85 delivered for them. I've used them before and it's a very easy tool to use (borrowed it off a Toymods member because I couldn't justify spending $85 on a tool that will be used once).
I don't have access to the tool anymore, but needed to take my valves out again and I've used a deep socket which is used to take spark plugs out. Fits right over 4AGE valve holders/keepers and just push down, comes right out. Just make sure you've got a small magnet hanging off the socket so that the keepers don't go flying.