I used the dual springs that were recommended and supplied by BPNW to match the cam. All of the springs were pressure tested and the readings were very uniform across the board.
The spring heights were all matched by using a custom made shim for each on the bottom of the spring, rather than having the bare spring ride on the head.
The machinist took the original inner spring guide/retainers and machined them to fit the new inners to keep them from walking sideways on the shims at high rpms.
This is not work that would, or could normally be accomplished without having a fully equipped machine shop and the knowledgeable people who know how and more importantly why, to do this type work.
I also had the the guides machined and new valve seals installed.