Grind that slot like 2 inches deeper and ya got a valvespring compressor tool where u can reach in and grab the keepers with a magnet....
make a little stub on the end and u can chuck it in your drill press,and use your drill press to compress the springs...
i got 2 drill presses..a beater one and a nice one
yea even at my old engine shop,they used an adjustable wrench,but on the reassembly they used the ground out socket,as described