Can you wiggle the valves? The guides are probably worn also. New stock SBC springs would be good to put on. It can be done without pulling the head.
You need to get the tool that bolts onto the rocker stud to compress the springs. Use a fitting into the sparkplug hole and use compressed air to blow into cylinder to hold the valves up while you change the springs. Doing it with this method will let you do one cylinder at a time. Tom
