pushrod length(s)

As BJR said, if you know the cam type, head type, and year, you should be able to call any good manufacturer and they can tell you what length you should need. I like to measure because then if things are milled, or thinner/thicker gaskets are used, etc., it's all taken into account. Then you just call and say "I need X length with ball and ball" or "ball and socket".