How do I match a valve spring

[hoosierdaddy]

i just picked up a 72 Duster with a never run 318 w/340 J heads motor , the PO left out the center valve springs for break in . I did a physical count last night and realized I'm missing one center spring . So how do I match up the spring to get the correct replacement .

 

[GeorgeH]

You would have to measure them with a spring tester. Comp and Crane have the inners listed in their cataloglogs. Crane's catalog is a little more comprehensive.
COMP Cams - Performance Camshafts, Lifters, Valve Springs, Rocker Arms p296 to give an example.

 

[hoosierdaddy]

Thanks