Front spring lenght question

I have looked in the search section and could not find the answer. I'm building a suicide front end the inside dimensions is 36.25 inches. I'm buying the perches and hangers from speedway. What lenght spring should I buy.
I've heard 5 inches shorter,,,maybe 31 inches. I just don't know, and would hate to buy the wrong one.

Thanks in advance.
John

 

Spring length is usually determined by measuring from the center line of the perch pin shackle hole to the opposite perch pin shackle hole and then subtracting 3" from the measurement to compensate for the shackles. example 36" minus 3" = 33" spring

 

There is a "Tip for measuring for a spring" in the speedway catalog. Since your using the perchs and hangers from them I'd go with their recommendations.