Solid Flat Tappet Valve Springs

The sweep across the valve tip looks good. I spoke with Howards today and they said 335# open was not enough. The engine doesn't miss or break up at rpm. Tech sat its beginning to flat and cant control the cylinder pressure.
I'm looking for a dual spring with 1.800 installed 360 -375# open pressure. Along with retainers for 11/32 valve with 10* keepers. Hughes has a spring from Pac but the retainers say +.100.
I run a trickflow dual spring in my SFT cammed 360 7k no problem TFS-16893-16 installed at 1.80