Need help picking out stock valve springs 289

Hello I’m refreshing a 289 out of a 1967 mustang fastback for a friend of the family’s. Oppon disassembling the heads I found one of the original valve springs was broken. There’s two different types of valve springs available one says “ after L-10 to L-14” and the other says “after L-14 change” I honestly have no clue what this means and I need help picking out the right springs for the engine I’m working on.