From the Blueprint specs in the Chrysler Racing Manual, Valve Springs
Load Closed Height Closed Load Open Height Open
273-2 bbl 74 1.62 150 1.31
273-4 bbl 103 1.62 184 1.31
That may be true but that isn't a factory parts book and may not reflect actual production.
There are an endless availability of aftermarket springs, Mopar Performance or other.
Show me Chrysler literature from 64-67 showing this information.