A slick cheap way on OHV heads, is to sacrifice a deep well socket that fits good over the spring collar, & use a C clamp.
You just need to open the sides up 180* apart at the tip of the socket, with a die grinder/ cut off wheel ect. , large enough to get the keepers & magnet in through, '' Magnet like on a pocket screwdriver''.
If worried about the socket flying out, you can use a hose clamp ect. to secure it to the end of the C clamp disc.