If you do need to change the springs there is a tool available that allows you to leave the head on. With it you end up changing 4 springs on 2 different cylinders at the same time. It only takes about an hour to change all 16. Mancini sells the tool.

Rule of thumb: If you're running a 5/16 fuel line, you only need a single spring. If you're running a 3/8 fuel line you need a double spring. Oh, and don't forget to line up the dots on the springs and retainers otherwise your spring timing will be retarded.