When I mean larger spring, I not only mean larger OD and height but I also include larger wire diameter.
In order to use a spring with a larger wire diameter, it must be a taller spring or compromise the coil bind or use a camshaft with less lift.
Well spit! A high lift camshaft was what you wanted in the first place or you would not have been trying to fit a larger and stronger valve spring. Right?
Lets go to dual springs then and keep the small wire diameter so not to compromise the coil bind height, Doggone it! You must have a larger diameter outer spring to accept the inner spring. Right?