Hey Luke I noticed the high riser heads are double springs on the valves. I recently had mine worked on (clean up some guides and install new seals) and they had TRIPLE springs.
How stiff were they? They were SO stiff the machinist couldn't use his normal air powered valve compression tool. He had to rig up some kind of "press" to assemble them.
Roller cam, rockers, etc. MEAN idle below 2000, runs in the 11's at the strip.